Module java.base

Package java.lang.runtime

Class TemplateRuntime

java.lang.Object

java.lang.runtime.TemplateRuntime

public final class TemplateRuntime
extends Object

TemplateRuntime is a preview API of the Java platform.

Programs can only use TemplateRuntime when preview features are enabled.

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

Manages string template bootstrap methods. These methods may be used, for example, by Java compiler implementations to create StringTemplate^PREVIEW instances. For example, the java compiler will translate the following code;

int x = 10;
int y = 20;
StringTemplate st = RAW."\{x} + \{y} = \{x + y}";

to byte code that invokes the newStringTemplate(java.lang.invoke.MethodHandles.Lookup, java.lang.String, java.lang.invoke.MethodType, java.lang.String...) bootstrap method to construct a CallSite that accepts two integers and produces a new StringTemplate^PREVIEW instance.

MethodHandles.Lookup lookup = MethodHandles.lookup();
MethodType mt = MethodType.methodType(StringTemplate.class, int.class, int.class);
CallSite cs = TemplateRuntime.newStringTemplate(lookup, "", mt, "", " + ", " = ", "");
...
int x = 10;
int y = 20;
StringTemplate st = (StringTemplate)cs.getTarget().invokeExact(x, y);

If the string template requires more than StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS^PREVIEW value slots, then the java compiler will use the newLargeStringTemplate(java.lang.invoke.MethodHandles.Lookup, java.lang.String, java.lang.invoke.MethodType) bootstrap method instead. For example, the java compiler will translate the following code;

int[] a = new int[1000], b = new int[1000];
...
StringTemplate st = """
     \{a[0]} - \{b[0]}
     \{a[1]} - \{b[1]}
     ...
     \{a[999]} - \{b[999]}
     """;

to byte code that invokes the newLargeStringTemplate(java.lang.invoke.MethodHandles.Lookup, java.lang.String, java.lang.invoke.MethodType) bootstrap method to construct a CallSite that accepts an array of integers and produces a new StringTemplate^PREVIEW instance.

MethodType mt = MethodType.methodType(StringTemplate.class, String[].class, Object[].class);
CallSite cs = TemplateRuntime.newStringTemplate(lookup, "", mt);
...
int[] a = new int[1000], b = new int[1000];
...
StringTemplate st = (StringTemplate)cs.getTarget().invokeExact(
        new String[] { "", " - ", "\n", " - ", "\n", ... " - ", "\n" },
        new Object[] { a[0], b[0], a[1], b[1], ..., a[999], b[999]}
        );

Since:

21

Method Summary

Modifier and Type	Method	Description
static CallSite	newLargeStringTemplate(MethodHandles.Lookup lookup, String name, MethodType type)	String template bootstrap method for creating large string templates, i.e., when the number of value slots exceeds StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTSPREVIEW.
static CallSite	newStringTemplate(MethodHandles.Lookup lookup, String name, MethodType type, String... fragments)	String template bootstrap method for creating string templates.
static CallSite	processStringTemplate(MethodHandles.Lookup lookup, String name, MethodType type, MethodHandle processorGetter, String... fragments)	String template bootstrap method for static final processors.

Methods declared in class java.lang.Object

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

Method Details

newStringTemplate

public static CallSite newStringTemplate(MethodHandles.Lookup lookup,
 String name,
 MethodType type,
 String... fragments)
                                  throws Throwable

String template bootstrap method for creating string templates. The static arguments include the fragments list. The non-static arguments are the values.

Parameters:

lookup - method lookup from call site

name - method name - not used

type - method type (ptypes...) -> StringTemplate

fragments - fragment array for string template

Returns:

CallSite to handle create string template

Throws:

NullPointerException - if any of the arguments is null

Throwable - if linkage fails

newLargeStringTemplate

public static CallSite newLargeStringTemplate(MethodHandles.Lookup lookup,
 String name,
 MethodType type)
                                       throws Throwable

String template bootstrap method for creating large string templates, i.e., when the number of value slots exceeds StringConcatFactory.MAX_INDY_CONCAT_ARG_SLOTS^PREVIEW. The non-static arguments are the fragments array and values array.

Parameters:

lookup - method lookup from call site

name - method name - not used

type - method type (String[], Object[]) -> StringTemplate

Returns:

CallSite to handle create large string template

Throws:

NullPointerException - if any of the arguments is null

Throwable - if linkage fails

processStringTemplate

public static CallSite processStringTemplate(MethodHandles.Lookup lookup,
 String name,
 MethodType type,
 MethodHandle processorGetter,
 String... fragments)
                                      throws Throwable

String template bootstrap method for static final processors. The static arguments include the fragments array and a MethodHandle to retrieve the value of the static final processor. The non-static arguments are the values.

Implementation Note:

this method is likely to be revamped before exiting preview.

Parameters:

lookup - method lookup from call site

name - method name - not used

type - method type (ptypes...) -> Object

processorGetter - MethodHandle to get static final processor

fragments - fragments from string template

Returns:

CallSite to handle string template processing

Throws:

NullPointerException - if any of the arguments is null

Throwable - if linkage fails