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 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 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