Class SwitchBootstraps

java.lang.Object

java.lang.runtime.SwitchBootstraps

public class SwitchBootstraps extends Object

SwitchBootstraps is a preview API of the Java platform.

Programs can only use SwitchBootstraps when preview features are enabled.

Preview features may be removed in a future release, or upgraded to permanent features of the Java platform.

Bootstrap methods for linking invokedynamic call sites that implement the selection functionality of the switch statement. The bootstraps take additional static arguments corresponding to the case labels of the switch, implicitly numbered sequentially from [0..N).

Since:: 17

Method Summary

Modifier and Type	Method	Description
`static CallSite`	`enumSwitch(MethodHandles.Lookup lookup, String invocationName, MethodType invocationType, Object... labels)`	Bootstrap method for linking an `invokedynamic` call site that implements a `switch` on a target of an enum type.
`static CallSite`	`typeSwitch(MethodHandles.Lookup lookup, String invocationName, MethodType invocationType, Object... labels)`	Bootstrap method for linking an `invokedynamic` call site that implements a `switch` on a target of a reference type.

Methods declared in class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Details

typeSwitch

public static CallSite typeSwitch(MethodHandles.Lookup lookup, String invocationName, MethodType invocationType, Object... labels)

Bootstrap method for linking an invokedynamic call site that implements a switch on a target of a reference type. The static arguments are an array of case labels which must be non-null and of type String or Integer or Class.

The type of the returned CallSite's method handle will have a return type of int. It has two parameters: the first argument will be an Object instance (target) and the second will be int (restart).

If the target is null, then the method of the call site returns -1.

If the target is not null, then the method of the call site returns the index of the first element in the labels array starting from the restart index matching one of the following conditions:

the element is of type Class that is assignable from the target's class; or
the element is of type String or Integer and equals to the target.

If no element in the labels array matches the target, then the method of the call site return the length of the labels array.

Parameters:: lookup - Represents a lookup context with the accessibility privileges of the caller. When used with invokedynamic, this is stacked automatically by the VM.; invocationName - unused; invocationType - The invocation type of the CallSite with two parameters, a reference type, an int, and int as a return type.; labels - case labels - String and Integer constants and Class instances, in any combination
Returns:: a CallSite returning the first matching element as described above
Throws:: NullPointerException - if any argument is null; IllegalArgumentException - if any element in the labels array is null, if the invocation type is not not a method type of first parameter of a reference type, second parameter of type int and with int as its return type, or if labels contains an element that is not of type String, Integer or Class.
See Java Virtual Machine Specification:: 4.4.6 The CONSTANT_NameAndType_info Structure
4.4.10 The CONSTANT_Dynamic_info and CONSTANT_InvokeDynamic_info Structures

enumSwitch

public static CallSite enumSwitch(MethodHandles.Lookup lookup, String invocationName, MethodType invocationType, Object... labels)

Bootstrap method for linking an invokedynamic call site that implements a switch on a target of an enum type. The static arguments are used to encode the case labels associated to the switch construct, where each label can be encoded in two ways:

as a String value, which represents the name of the enum constant associated with the label
as a Class value, which represents the enum type associated with a type test pattern

The returned CallSite's method handle will have a return type of int and accepts two parameters: the first argument will be an Enum instance (target) and the second will be int (restart).

If the target is null, then the method of the call site returns -1.

the element is of type Class that is assignable from the target's class; or
the element is of type String and equals to the target enum constant's Enum.name().

If no element in the labels array matches the target, then the method of the call site return the length of the labels array.

Parameters:: lookup - Represents a lookup context with the accessibility privileges of the caller. When used with invokedynamic, this is stacked automatically by the VM.; invocationName - unused; invocationType - The invocation type of the CallSite with two parameters, an enum type, an int, and int as a return type.; labels - case labels - String constants and Class instances, in any combination
Returns:: a CallSite returning the first matching element as described above
Throws:: NullPointerException - if any argument is null; IllegalArgumentException - if any element in the labels array is null, if the invocation type is not a method type whose first parameter type is an enum type, second parameter of type int and whose return type is int, or if labels contains an element that is not of type String or Class of the target enum type.
See Java Virtual Machine Specification:: 4.4.6 The CONSTANT_NameAndType_info Structure
4.4.10 The CONSTANT_Dynamic_info and CONSTANT_InvokeDynamic_info Structures

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/17/docs/api/java.base/java/lang/runtime/SwitchBootstraps.html