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/OpenJDK 21

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 StringTemplatePREVIEW 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 StringTemplatePREVIEW 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_SLOTSPREVIEW 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 StringTemplatePREVIEW 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_SLOTSPREVIEW. 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

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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.
Various third party code in OpenJDK is licensed under different licenses (see Debian package).
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/lang/runtime/TemplateRuntime.html