JSHELL(1) JDK Commands JSHELL(1)
NAME
jshell - interactively evaluate declarations, statements, and expres-
sions of the Java programming language in a read-eval-print loop (REPL)
SYNOPSIS
jshell [options] [load-files]
options
Command-line options, separated by spaces. See Options for
jshell.
load-files
One or more scripts to run when the tool is started. Scripts
can contain any valid code snippets or JShell commands.
The script can be a local file or one of following predefined
scripts:
DEFAULT
Loads the default entries, which are commonly used as im-
ports.
JAVASE Imports all Java SE packages.
PRINTING
Defines print, println, and printf as jshell methods for
use within the tool.
TOOLING
Defines javac, jar, and other methods for running JDK
tools via their command-line interface within the jshell
tool.
For more than one script, use a space to separate the names.
Scripts are run in the order in which they're entered on the
command line. Command-line scripts are run after startup
scripts. To run a script after JShell is started, use the /open
command.
To accept input from standard input and suppress the interactive
I/O, enter a hyphen (-) for load-files. This option enables the
use of the jshell tool in pipe chains.
DESCRIPTION
JShell provides a way to interactively evaluate declarations, state-
ments, and expressions of the Java programming language, making it eas-
ier to learn the language, explore unfamiliar code and APIs, and proto-
type complex code. Java statements, variable definitions, method defi-
nitions, class definitions, import statements, and expressions are ac-
cepted. The bits of code entered are called snippets.
As snippets are entered, they're evaluated, and feedback is provided.
Feedback varies from the results and explanations of actions to noth-
ing, depending on the snippet entered and the feedback mode chosen.
Errors are described regardless of the feedback mode. Start with the
verbose mode to get the most feedback while learning the tool.
Command-line options are available for configuring the initial environ-
ment when JShell is started. Within JShell, commands are available for
modifying the environment as needed.
Existing snippets can be loaded from a file to initialize a JShell ses-
sion, or at any time within a session. Snippets can be modified within
the session to try out different variations and make corrections. To
keep snippets for later use, save them to a file.
OPTIONS FOR JSHELL
--add-exports module/package
Specifies a package to be considered as exported from its defin-
ing module.
--add-modules module[,module...]
Specifies the root modules to resolve in addition to the initial
module.
-Cflag Provides a flag to pass to the compiler. To pass more than one
flag, provide an instance of this option for each flag or flag
argument needed.
--class-path path
Specifies the directories and archives that are searched to lo-
cate class files. This option overrides the path in the CLASS-
PATH environment variable. If the environment variable isn't
set and this option isn't used, then the current directory is
searched. For Linux and macOS, use a colon (:) to separate
items in the path. For Windows, use a semicolon (;) to separate
items.
--enable-preview
Allows code to depend on the preview features of this release.
--execution specification
Specifies an alternate execution engine, where specification is
an ExecutionControl spec. See the documentation of the package
jdk.jshell.spi for the syntax of the spec.
--feedback mode
Sets the initial level of feedback provided in response to
what's entered. The initial level can be overridden within a
session by using the /set feedback mode command. The default is
normal.
The following values are valid for mode:
verbose
Provides detailed feedback for entries. Additional in-
formation about the action performed is displayed after
the result of the action. The next prompt is separated
from the feedback by a blank line.
normal Provides an average amount of feedback. The next prompt
is separated from the feedback by a blank line.
concise
Provides minimal feedback. The next prompt immediately
follows the code snippet or feedback.
silent Provides no feedback. The next prompt immediately fol-
lows the code snippet.
custom Provides custom feedback based on how the mode is de-
fined. Custom feedback modes are created within JShell
by using the /set mode command.
--help or -h or -?
Prints a summary of standard options and exits the tool.
--help-extra or -X
Prints a summary of nonstandard options and exits the tool.
Nonstandard options are subject to change without notice.
-Jflag Provides a flag to pass to the runtime system. To pass more
than one flag, provide an instance of this option for each flag
or flag argument needed.
--module-path modulepath
Specifies where to find application modules. For Linux and mac-
OS, use a colon (:) to separate items in the path. For Windows,
use a semicolon (;) to separate items.
--no-startup
Prevents startup scripts from running when JShell starts. Use
this option to run only the scripts entered on the command line
when JShell is started, or to start JShell without any preloaded
information if no scripts are entered. This option can't be
used if the --startup option is used.
-q Sets the feedback mode to concise, which is the same as entering
--feedback concise.
-Rflag Provides a flag to pass to the remote runtime system. To pass
more than one flag, provide an instance of this option for each
flag or flag argument to pass.
-s Sets the feedback mode to silent, which is the same as entering
--feedback silent.
--show-version
Prints version information and enters the tool.
--startup file
Overrides the default startup script for this session. The
script can contain any valid code snippets or commands.
The script can be a local file or one of the following prede-
fined scripts:
DEFAULT
Loads the default entries, which are commonly used as im-
ports.
JAVASE Imports all Java SE packages.
PRINTING
Defines print, println, and printf as jshell methods for
use within the tool.
TOOLING
Defines javac, jar, and other methods for running JDK
tools via their command-line interface within the jshell
tool.
For more than one script, provide a separate instance of this
option for each script. Startup scripts are run when JShell is
first started and when the session is restarted with the /reset,
/reload, or /env command. Startup scripts are run in the order
in which they're entered on the command line.
This option can't be used if the --no-startup option is used.
-v Sets the feedback mode to verbose, which is the same as entering
--feedback verbose.
--version
Prints version information and exits the tool.
JSHELL COMMANDS
Within the jshell tool, commands are used to modify the environment and
manage code snippets.
/drop {name|id|startID-endID} [{name|id|startID-endID}...]
Drops snippets identified by name, ID, or ID range, making them
inactive. For a range of IDs, provide the starting ID and end-
ing ID separated with a hyphen. To provide a list, separate the
items in the list with a space. Use the /list command to see
the IDs of code snippets.
/edit [option]
Opens an editor. If no option is entered, then the editor opens
with the active snippets.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Opens the editor with the snippets identified by name,
ID, or ID range. For a range of IDs, provide the start-
ing ID and ending ID separated with a hyphen. To provide
a list, separate the items in the list with a space. Use
the /list command to see the IDs of code snippets.
-all Opens the editor with all snippets, including startup
snippets and snippets that failed, were overwritten, or
were dropped.
-start Opens the editor with startup snippets that were evaluat-
ed when JShell was started.
To exit edit mode, close the editor window, or respond to the
prompt provided if the -wait option was used when the editor was
set.
Use the /set editor command to specify the editor to use. If no
editor is set, then the following environment variables are
checked in order: JSHELLEDITOR, VISUAL, and EDITOR. If no edi-
tor is set in JShell and none of the editor environment vari-
ables is set, then a simple default editor is used.
/env [options]
Displays the environment settings, or updates the environment
settings and restarts the session. If no option is entered,
then the current environment settings are displayed. If one or
more options are entered, then the session is restarted as fol-
lows:
• Updates the environment settings with the provided options.
• Resets the execution state.
• Runs the startup scripts.
• Silently replays the history in the order entered. The histo-
ry includes all valid snippets or /drop commands entered at
the jshell prompt, in scripts entered on the command line, or
scripts entered with the /open command.
Environment settings entered on the command line or provided
with a previous /reset, /env, or /reload command are maintained
unless an option is entered that overwrites the setting.
The following options are valid:
--add-modules module[,module...]
Specifies the root modules to resolve in addition to the
initial module.
--add-exports source-module/package=target-module[,target-mod-
ule]*
Adds an export of package from source-module to target-
module.
--class-path path
Specifies the directories and archives that are searched
to locate class files. This option overrides the path in
the CLASSPATH environment variable. If the environment
variable isn't set and this option isn't used, then the
current directory is searched. For Linux and macOS, use
a colon (:) to separate items in the path. For Windows,
use a semicolon (;) to separate items.
--module-path modulepath
Specifies where to find application modules. For Linux
and macOS, use a colon (:) to separate items in the path.
For Windows, use a semicolon (;) to separate items.
/exit [integer-expression-snippet]
Exits the tool. If no snippet is entered, the exit status is
zero. If a snippet is entered and the result of the snippet is
an integer, the result is used as the exit status. If an error
occurs, or the result of the snippet is not an integer, an error
is displayed and the tool remains active.
/history
Displays what was entered in this session.
/help [command|subject]
Displays information about commands and subjects. If no options
are entered, then a summary of information for all commands and
a list of available subjects are displayed. If a valid command
is provided, then expanded information for that command is dis-
played. If a valid subject is entered, then information about
that subject is displayed.
The following values for subject are valid:
context
Describes the options that are available for configuring
the environment.
intro Provides an introduction to the tool.
shortcuts
Describes keystrokes for completing commands and snip-
pets. See Input Shortcuts.
/imports
Displays the current active imports, including those from the
startup scripts and scripts that were entered on the command
line when JShell was started.
/list [option]
Displays a list of snippets and their IDs. If no option is en-
tered, then all active snippets are displayed, but startup snip-
pets aren't.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Displays the snippets identified by name, ID, or ID
range. For a range of IDs, provide the starting ID and
ending ID separated with a hyphen. To provide a list,
separate the items in the list with a space.
-all Displays all snippets, including startup snippets and
snippets that failed, were overwritten, or were dropped.
IDs that begin with s are startup snippets. IDs that be-
gin with e are snippets that failed.
-start Displays startup snippets that were evaluated when JShell
was started.
/methods [option]
Displays information about the methods that were entered. If no
option is entered, then the name, parameter types, and return
type of all active methods are displayed.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Displays information for methods identified by name, ID,
or ID range. For a range of IDs, provide the starting ID
and ending ID separated with a hyphen. To provide a
list, separate the items in the list with a space. Use
the /list command to see the IDs of code snippets.
-all Displays information for all methods, including those
added when JShell was started, and methods that failed,
were overwritten, or were dropped.
-start Displays information for startup methods that were added
when JShell was started.
/open file
Opens the script specified and reads the snippets into the tool.
The script can be a local file or one of the following prede-
fined scripts:
DEFAULT
Loads the default entries, which are commonly used as im-
ports.
JAVASE Imports all Java SE packages.
PRINTING
Defines print, println, and printf as jshell methods for
use within the tool.
TOOLING
Defines javac, jar, and other methods for running JDK
tools via their command-line interface within the jshell
tool.
/reload [options]
Restarts the session as follows:
• Updates the environment settings with the provided options, if
any.
• Resets the execution state.
• Runs the startup scripts.
• Replays the history in the order entered. The history in-
cludes all valid snippets or /drop commands entered at the
jshell prompt, in scripts entered on the command line, or
scripts entered with the /open command.
Environment settings entered on the command line or provided
with a previous /reset, /env, or /reload command are maintained
unless an option is entered that overwrites the setting.
The following options are valid:
--add-modules module[,module...]
Specifies the root modules to resolve in addition to the
initial module.
--add-exports source-module/package=target-module[,target-mod-
ule]*
Adds an export of package from source-module to target-
module.
--class-path path
Specifies the directories and archives that are searched
to locate class files. This option overrides the path in
the CLASSPATH environment variable. If the environment
variable isn't set and this option isn't used, then the
current directory is searched. For Linux and macOS, use
a colon (:) to separate items in the path. For Windows,
use a semicolon (;) to separate items.
--module-path modulepath
Specifies where to find application modules. For Linux
and macOS, use a colon (:) to separate items in the path.
For Windows, use a semicolon (;) to separate items.
-quiet Replays the valid history without displaying it. Errors
are displayed.
-restore
Resets the environment to the state at the start of the
previous run of the tool or to the last time a /reset,
/reload, or /env command was executed in the previous
run. The valid history since that point is replayed.
Use this option to restore a previous JShell session.
/reset [options]
Discards all entered snippets and restarts the session as fol-
lows:
• Updates the environment settings with the provided options, if
any.
• Resets the execution state.
• Runs the startup scripts.
History is not replayed. All code that was entered is lost.
Environment settings entered on the command line or provided
with a previous /reset, /env, or /reload command are maintained
unless an option is entered that overwrites the setting.
The following options are valid:
--add-modules module[,module...]
Specifies the root modules to resolve in addition to the
initial module.
--add-exports source-module/package=target-module[,target-mod-
ule]*
Adds an export of package from source-module to target-
module.
--class-path path
Specifies the directories and archives that are searched
to locate class files. This option overrides the path in
the CLASSPATH environment variable. If the environment
variable isn't set and this option isn't used, then the
current directory is searched. For Linux and macOS, use
a colon (:) to separate items in the path. For Windows,
use a semicolon (;) to separate items.
--module-path modulepath
Specifies where to find application modules. For Linux
and macOS, use a colon (:) to separate items in the path.
For Windows, use a semicolon (;) to separate items.
/save [options] file
Saves snippets and commands to the file specified. If no op-
tions are entered, then active snippets are saved.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Saves the snippets and commands identified by name, ID,
or ID range. For a range of IDs, provide the starting ID
and ending ID separated with a hyphen. To provide a
list, separate the items in the list with a space. Use
the /list command to see the IDs of the code snippets.
-all Saves all snippets, including startup snippets and snip-
pets that were overwritten or failed.
-history
Saves the sequential history of all commands and snippets
entered in the current session.
-start Saves the current startup settings. If no startup
scripts were provided, then an empty file is saved.
/set [setting]
Sets configuration information, including the external editor,
startup settings, and feedback mode. This command is also used
to create a custom feedback mode with customized prompt, format,
and truncation values. If no setting is entered, then the cur-
rent setting for the editor, startup settings, and feedback mode
are displayed.
The following values are valid for setting:
editor [options] [command]
Sets the command used to start an external editor when
the /edit command is entered. The command can include
command arguments separated by spaces. If no command or
options are entered, then the current setting is dis-
played.
The following options are valid:
-default
Sets the editor to the default editor provided
with JShell. This option can't be used if a com-
mand for starting an editor is entered.
-delete
Sets the editor to the one in effect when the ses-
sion started. If used with the -retain option,
then the retained editor setting is deleted and
the editor is set to the first of the following
environment variables found: JSHELLEDITOR, VISUAL,
or EDITOR. If none of the editor environment
variables are set, then this option sets the edi-
tor to the default editor.
This option can't be used if a command for start-
ing an editor is entered.
-retain
Saves the editor setting across sessions. If no
other option or a command is entered, then the
current setting is saved.
-wait Prompts the user to indicate when editing is com-
plete. Otherwise control returns to JShell when
the editor exits. Use this option if the editor
being used exits immediately, for example, when an
edit window already exists. This option is valid
only when a command for starting an editor is en-
tered.
feedback [mode]
Sets the feedback mode used to respond to input. If no
mode is entered, then the current mode is displayed.
The following modes are valid: concise, normal, silent,
verbose, and any custom mode created with the /set mode
command.
format mode field "format-string" selector
Sets the format of the feedback provided in response to
input. If no mode is entered, then the current formats
for all fields for all feedback modes are displayed. If
only a mode is entered, then the current formats for that
mode are displayed. If only a mode and field are en-
tered, then the current formats for that field are dis-
played.
To define a format, the following arguments are required:
mode Specifies a feedback mode to which the response
format is applied. Only custom modes created with
the /set mode command can be modified.
field Specifies a context-specific field to which the
response format is applied. The fields are de-
scribed in the online help, which is accessed from
JShell using the /help /set format command.
"format-string"
Specifies the string to use as the response format
for the specified field and selector. The struc-
ture of the format string is described in the on-
line help, which is accessed from JShell using the
/help /set format command.
selector
Specifies the context in which the response format
is applied. The selectors are described in the
online help, which is accessed from JShell using
the /help /set format command.
mode [mode-name] [existing-mode] [options]
Creates a custom feedback mode with the mode name provid-
ed. If no mode name is entered, then the settings for
all modes are displayed, which includes the mode, prompt,
format, and truncation settings. If the name of an ex-
isting mode is provided, then the settings from the ex-
isting mode are copied to the mode being created.
The following options are valid:
-command|-quiet
Specifies the level of feedback displayed for com-
mands when using the mode. This option is re-
quired when creating a feedback mode. Use -com-
mand to show information and verification feedback
for commands. Use -quiet to show only essential
feedback for commands, such as error messages.
-delete
Deletes the named feedback mode for this session.
The name of the mode to delete is required. To
permanently delete a retained mode, use the -re-
tain option with this option. Predefined modes
can't be deleted.
-retain
Saves the named feedback mode across sessions.
The name of the mode to retain is required.
Configure the new feedback mode using the /set prompt,
/set format, and /set truncation commands.
To start using the new mode, use the /set feedback com-
mand.
prompt mode "prompt-string" "continuation-prompt-string"
Sets the prompts for input within JShell. If no mode is
entered, then the current prompts for all feedback modes
are displayed. If only a mode is entered, then the cur-
rent prompts for that mode are displayed.
To define a prompt, the following arguments are required:
mode Specifies the feedback mode to which the prompts
are applied. Only custom modes created with the
/set mode command can be modified.
"prompt-string"
Specifies the string to use as the prompt for the
first line of input.
"continuation-prompt-string"
Specifies the string to use as the prompt for the
additional input lines needed to complete a snip-
pet.
start [-retain] [file [file...]|option]
Sets the names of the startup scripts used when the next
/reset, /reload, or /env command is entered. If more
than one script is entered, then the scripts are run in
the order entered. If no scripts or options are entered,
then the current startup settings are displayed.
The scripts can be local files or one of the following
predefined scripts:
DEFAULT
Loads the default entries, which are commonly used
as imports.
JAVASE Imports all Java SE packages.
PRINTING
Defines print, println, and printf as jshell meth-
ods for use within the tool.
TOOLING
Defines javac, jar, and other methods for running
JDK tools via their command-line interface within
the jshell tool.
The following options are valid:
-default
Sets the startup settings to the default settings.
-none Specifies that no startup settings are used.
Use the -retain option to save the start setting across
sessions.
truncation mode length selector
Sets the maximum length of a displayed value. If no mode
is entered, then the current truncation values for all
feedback modes are displayed. If only a mode is entered,
then the current truncation values for that mode are dis-
played.
To define truncation values, the following arguments are
required:
mode Specifies the feedback mode to which the trunca-
tion value is applied. Only custom modes created
with the /set mode command can be modified.
length Specifies the unsigned integer to use as the maxi-
mum length for the specified selector.
selector
Specifies the context in which the truncation val-
ue is applied. The selectors are described in the
online help, which is accessed from JShell using
the /help /set truncation command.
/types [option]
Displays classes, interfaces, and enums that were entered. If
no option is entered, then all current active classes, inter-
faces, and enums are displayed.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Displays information for classes, interfaces, and enums
identified by name, ID, or ID range. For a range of IDs,
provide the starting ID and ending ID separated with a
hyphen. To provide a list, separate the items in the
list with a space. Use the /list command to see the IDs
of the code snippets.
-all Displays information for all classes, interfaces, and
enums, including those added when JShell was started, and
classes, interfaces, and enums that failed, were over-
written, or were dropped.
-start Displays information for startup classes, interfaces, and
enums that were added when JShell was started.
/vars [option]
Displays the name, type, and value of variables that were en-
tered. If no option is entered, then all current active vari-
ables are displayed.
The following options are valid:
{name|id|startID-endID} [{name|id|startID-endID}...]
Displays information for variables identified by name,
ID, or ID range. For a range of IDs, provide the start-
ing ID and ending ID separated with a hyphen. To provide
a list, separate the items in the list with a space. Use
the /list command to see the IDs of the code snippets.
-all Displays information for all variables, including those
added when JShell was started, and variables that failed,
were overwritten, or were dropped.
-start Displays information for startup variables that were
added when JShell was started.
/? Same as the /help command.
/! Reruns the last snippet.
/{name|id|startID-endID} [{name|id|startID-endID}...]
Reruns the snippets identified by ID, range of IDs, or name.
For a range of IDs, provide the starting ID and ending ID sepa-
rated with a hyphen. To provide a list, separate the items in
the list with a space. The first item in the list must be an ID
or ID range. Use the /list command to see the IDs of the code
snippets.
/-n Reruns the -nth previous snippet. For example, if 15 code snip-
pets were entered, then /-4 runs the 11th snippet. Commands
aren't included in the count.
INPUT SHORTCUTS
The following shortcuts are available for entering commands and snip-
pets in JShell.
Tab completion
<tab> When entering snippets, commands, subcommands, command argu-
ments, or command options, use the Tab key to automatically com-
plete the item. If the item can't be determined from what was
entered, then possible options are provided.
When entering a method call, use the Tab key after the method
call's opening parenthesis to see the parameters for the method.
If the method has more than one signature, then all signatures
are displayed. Pressing the Tab key a second time displays the
description of the method and the parameters for the first sig-
nature. Continue pressing the Tab key for a description of any
additional signatures.
Shift+<Tab> V
After entering a complete expression, use this key sequence to
convert the expression to a variable declaration of a type de-
termined by the type of the expression.
Shift+<Tab> M
After entering a complete expression or statement, use this key
sequence to convert the expression or statement to a method dec-
laration. If an expression is entered, the return type is based
on the type of the expression.
Shift+<Tab> I
When an identifier is entered that can't be resolved, use this
key sequence to show possible imports that resolve the identifi-
er based on the content of the specified class path.
Command abbreviations
An abbreviation of a command is accepted if the abbreviation uniquely
identifies a command. For example, /l is recognized as the /list com-
mand. However, /s isn't a valid abbreviation because it can't be de-
termined if the /set or /save command is meant. Use /se for the /set
command or /sa for the /save command.
Abbreviations are also accepted for subcommands, command arguments, and
command options. For example, use /m -a to display all methods.
History navigation
A history of what was entered is maintained across sessions. Use the
up and down arrows to scroll through commands and snippets from the
current and past sessions. Use the Ctrl key with the up and down ar-
rows to skip all but the first line of multiline snippets.
History search
Use the Ctrl+R key combination to search the history for the string en-
tered. The prompt changes to show the string and the match. Ctrl+R
searches backwards from the current location in the history through
earlier entries. Ctrl+S searches forward from the current location in
the history though later entries.
INPUT EDITING
The editing capabilities of JShell are similar to that of other common
shells. Keyboard keys and key combinations provide line editing short-
cuts. The Ctrl key and Meta key are used in key combinations. If your
keyboard doesn't have a Meta key, then the Alt key is often mapped to
provide Meta key functionality.
Line Editing Shortcuts
Key or Key Combination Action
────────────────────────────────────────────────────
Return Enter the current line.
Left arrow Move the cursor to the
left one character.
Right arrow Move the cursor to the right
one character.
Ctrl+A Move the cursor to the be-
ginning of the line.
Ctrl+E Move the cursor to the end
of the line.
Meta+B Move the cursor to the
left one word.
Meta+F Move the cursor to the
right one word.
Delete Delete the character under
the cursor.
Backspace Delete the character be-
fore the cursor.
Ctrl+K Delete the text from the
cursor to the end of the
line.
Meta+D Delete the text from the
cursor to the end of the
word.
Ctrl+W Delete the text from the
cursor to the previous
white space.
Ctrl+Y Paste the most recently
deleted text into the
line.
Meta+Y After Ctrl+Y, press to cy-
cle through the previously
deleted text.
EXAMPLE OF STARTING AND STOPPING A JSHELL SESSION
JShell is provided with the JDK. To start a session, enter jshell on
the command line. A welcome message is printed, and a prompt for en-
tering commands and snippets is provided.
% jshell
| Welcome to JShell -- Version 9
| For an introduction type: /help intro
jshell>
To see which snippets were automatically loaded when JShell started,
use the /list -start command. The default startup snippets are import
statements for common packages. The ID for each snippet begins with
the letter s, which indicates it's a startup snippet.
jshell> /list -start
s1 : import java.io.*;
s2 : import java.math.*;
s3 : import java.net.*;
s4 : import java.nio.file.*;
s5 : import java.util.*;
s6 : import java.util.concurrent.*;
s7 : import java.util.function.*;
s8 : import java.util.prefs.*;
s9 : import java.util.regex.*;
s10 : import java.util.stream.*;
jshell>
To end the session, use the /exit command.
jshell> /exit
| Goodbye
%
EXAMPLE OF ENTERING SNIPPETS
Snippets are Java statements, variable definitions, method definitions,
class definitions, import statements, and expressions. Terminating
semicolons are automatically added to the end of a completed snippet if
they're missing.
The following example shows two variables and a method being defined,
and the method being run. Note that a scratch variable is automatical-
ly created to hold the result because no variable was provided.
jshell> int a=4
a ==> 4
jshell> int b=8
b ==> 8
jshell> int square(int i1) {
...> return i1 * i1;
...> }
| created method square(int)
jshell> square(b)
$5 ==> 64
EXAMPLE OF CHANGING SNIPPETS
Change the definition of a variable, method, or class by entering it
again.
The following examples shows a method being defined and the method run:
jshell> String grade(int testScore) {
...> if (testScore >= 90) {
...> return "Pass";
...> }
...> return "Fail";
...> }
| created method grade(int)
jshell> grade(88)
$3 ==> "Fail"
To change the method grade to allow more students to pass, enter the
method definition again and change the pass score to 80. Use the up
arrow key to retrieve the previous entries to avoid having to reenter
them and make the change in the if statement. The following example
shows the new definition and reruns the method to show the new result:
jshell> String grade(int testScore) {
...> if (testScore >= 80) {
...> return "Pass";
...> }
...> return "Fail";
...> }
| modified method grade(int)
jshell> grade(88)
$5 ==> "Pass"
For snippets that are more than a few lines long, or to make more than
a few changes, use the /edit command to open the snippet in an editor.
After the changes are complete, close the edit window to return control
to the JShell session. The following example shows the command and the
feedback provided when the edit window is closed. The /list command is
used to show that the pass score was changed to 85.
jshell> /edit grade
| modified method grade(int)
jshell> /list grade
6 : String grade(int testScore) {
if (testScore >= 85) {
return "Pass";
}
return "Fail";
}
EXAMPLE OF CREATING A CUSTOM FEEDBACK MODE
The feedback mode determines the prompt that's displayed, the feedback
messages that are provided as snippets are entered, and the maximum
length of a displayed value. Predefined feedback modes are provided.
Commands for creating custom feedback modes are also provided.
Use the /set mode command to create a new feedback mode. In the fol-
lowing example, the new mode mymode, is based on the predefined feed-
back mode, normal, and verifying command feedback is displayed:
jshell> /set mode mymode normal -command
| Created new feedback mode: mymode
Because the new mode is based on the normal mode, the prompts are the
same. The following example shows how to see what prompts are used and
then changes the prompts to custom strings. The first string repre-
sents the standard JShell prompt. The second string represents the
prompt for additional lines in multiline snippets.
jshell> /set prompt mymode
| /set prompt mymode "\njshell> " " ...> "
jshell> /set prompt mymode "\nprompt$ " " continue$ "
The maximum length of a displayed value is controlled by the truncation
setting. Different types of values can have different lengths. The
following example sets an overall truncation value of 72, and a trunca-
tion value of 500 for variable value expressions:
jshell> /set truncation mymode 72
jshell> /set truncation mymode 500 varvalue
The feedback displayed after snippets are entered is controlled by the
format setting and is based on the type of snippet entered and the ac-
tion taken for that snippet. In the predefined mode normal, the string
created is displayed when a method is created. The following example
shows how to change that string to defined:
jshell> /set format mymode action "defined" added-primary
Use the /set feedback command to start using the feedback mode that was
just created. The following example shows the custom mode in use:
jshell> /set feedback mymode
| Feedback mode: mymode
prompt$ int square (int num1){
continue$ return num1*num1;
continue$ }
| defined method square(int)
prompt$
JDK 21 2023 JSHELL(1)
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