Java 8 数组构造函数引用如何工作? [英] How do Java 8 array constructor references work?

问题描述

假设我们有一个 IntFunction 类型的变量，它返回一个整数数组:

Say we have a variable of type IntFunction that returns an integer array:

IntFunction<int[]> i;

使用 Java 8 泛型，可以使用这样的构造函数引用来初始化这个变量:

With Java 8 generics, it is possible to initialize this variable with a constructor reference like this:

i = int[]::new

Java 编译器如何将其转换为字节码?

How does the Java compiler translate this to bytecode?

我知道对于其他类型，例如 String::new，它可以使用一个 invokedynamic 指令指向 String 构造函数 java/lang/String.(...)，这只是一个有特殊意义的方法.

I know that for other types, like String::new, it can use an invokedynamic instruction that points to the String constructor java/lang/String.<init>(...), which is just a method with a special meaning.

这对数组是如何工作的，看到有构造数组的特殊说明?

How does this work with arrays, seeing that there are special instructions for constructing arrays?

推荐答案

你可以通过反编译java字节码来找出自己:

You can find out yourself by decompiling the java bytecode:

javap -c -v -p MyClass.class

编译器 desugars 数组构造函数将 Foo[]::new 引用到一个 lambda (i -> new Foo[i])，然后像任何其他 lambda 或方法参考.这是这个合成 lambda 的反汇编字节码:

The compiler desugars array constructor references Foo[]::new to a lambda (i -> new Foo[i]), and then proceeds as with any other lambda or method reference. Here's the disassembled bytecode of this synthetic lambda:

private static java.lang.Object lambda$MR$new$new$635084e0$1(int);
descriptor: (I)Ljava/lang/Object;
flags: ACC_PRIVATE, ACC_STATIC, ACC_SYNTHETIC
Code:
  stack=1, locals=1, args_size=1
     0: iload_0       
     1: anewarray     #6                  // class java/lang/String
     4: areturn       

(它的返回类型是Object，因为IntFunction中擦除的返回类型是Object.)

(It's return type is Object because the erased return type in IntFunction is Object.)

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