Package jdk.jshell
JShell
is the central class. An instance of
JShell
holds the evaluation state, which is both the current
set of source snippets and the execution state they have produced.
Each source snippet is represented by an instance of a subclass of
Snippet
. For example, a statement is represented by an
instance of StatementSnippet
, and a method declaration is
represented by an instance of MethodSnippet
.
Snippets are created when
JShell.eval(String)
is invoked with an input which includes one or more snippets of code.
Any change to the compilation status of a snippet is reported with a
SnippetEvent
. There are three major kinds of
changes to the status of a snippet: it can be created with eval
,
it can be dropped from the active source state with
JShell.drop(jdk.jshell.Snippet)
, and it can have
its status updated as a result of a status change in another snippet.
For
example: given js
, an instance of JShell
, executing
js.eval("int x = 5;")
will add the variable x
to
the source state and will generate an event describing the creation of a
VarSnippet
for x
. Then executing
js.eval("int timesx(int val) { return val * x; }")
will add
a method to the source state and will generate an event
describing the creation of a MethodSnippet
for
timesx
.
Assume that varx
holds the snippet created by the first
call to eval
, executing js.drop(varx)
will
generate two events: one for changing the status of the
variable snippet to DROPPED
and one for
updating the method snippet (which now has an unresolved reference to
x
).
Of course, for any general application of the API, the input would not be fixed strings, but would come from the user. Below is a very simplified example of how the API might be used to implement a REPL.
import java.io.ByteArrayInputStream;
import java.io.Console;
import java.util.List;
import jdk.jshell.*;
import jdk.jshell.Snippet.Status;
class ExampleJShell {
public static void main(String[] args) {
Console console = System.console();
try (JShell js = JShell.create()) {
do {
System.out.print("Enter some Java code: ");
String input = console.readLine();
if (input == null) {
break;
}
List<SnippetEvent> events = js.eval(input);
for (SnippetEvent e : events) {
StringBuilder sb = new StringBuilder();
if (e.causeSnippet() == null) {
// We have a snippet creation event
switch (e.status()) {
case VALID:
sb.append("Successful ");
break;
case RECOVERABLE_DEFINED:
sb.append("With unresolved references ");
break;
case RECOVERABLE_NOT_DEFINED:
sb.append("Possibly reparable, failed ");
break;
case REJECTED:
sb.append("Failed ");
break;
}
if (e.previousStatus() == Status.NONEXISTENT) {
sb.append("addition");
} else {
sb.append("modification");
}
sb.append(" of ");
sb.append(e.snippet().source());
System.out.println(sb);
if (e.value() != null) {
System.out.printf("Value is: %s\n", e.value());
}
System.out.flush();
}
}
} while (true);
}
System.out.println("\nGoodbye");
}
}
To register for status change events use
JShell.onSnippetEvent(java.util.function.Consumer)
.
These events are only generated by eval
and drop
,
the return values of these methods are the list of events generated by that
call. So, as in the example above, events can be used without registering
to receive events.
If you experiment with this example, you will see that failing to terminate
a statement or variable declaration with a semi-colon will simply fail.
An unfinished entry (for example a desired multi-line method) will also just
fail after one line. The utilities in SourceCodeAnalysis
provide source boundary and completeness analysis to address cases like
those. SourceCodeAnalysis
also provides suggested completions
of input, as might be used in tab-completion.
- Since:
- 9
-
ClassDescriptionGrouping for all declaration Snippets: variable declarations (
VarSnippet
), method declarations (MethodSnippet
), and type declarations (TypeDeclSnippet
).Diagnostic information for a Snippet.A snippet of code that is not valid Java programming language code.Wraps an throwable thrown in the executing client.Snippet for an assignment or variable-value expression.Snippet for an import declaration.The JShell evaluation state engine.Builder forJShell
instances.The superclass of JShell generated exceptionsSnippet for a method definition.Grouping for Snippets which persist and influence future code.A Snippet represents a snippet of Java source code as passed toJShell.eval(java.lang.String)
.Describes the general kind of snippet.Describes the current state of a Snippet.The detailed variety of a snippet.A description of a change to a Snippet.Provides analysis utilities for source code input.Describes the completeness of the given input.The result ofanalyzeCompletion(String input)
.A documentation for a candidate for continuation of the given user's input.List of possible qualified names.The wrapping of a snippet of Java source into valid top-level Java source.A candidate for continuation of the given user's input.Snippet for a statement.Snippet for a type definition (a class, interface, enum, or annotation interface definition).Exception reported on attempting to execute aRECOVERABLE_DEFINED
snippet.Snippet for a variable definition.