java - 使用对象状态调用方法的消费者

Question

这个问题已经有答案了:

Is Java "pass-by-reference" or "pass-by-value"? (90 个答案)

已关闭 4 年前。

我有课

public final class GGGGG {

    private final String str;

    public GGGGG(final String str) {
        this.str = str;
    }

    public void showElement(final String test){
        System.out.println(this.str+test);
    }

    public static void main(String[] args) {
        GGGGG hello = new GGGGG("hello");
        final Test2 test2 = new Test2(hello::showElement);
        test2.test();
        hello = null;
        test2.test();

    }

    static class Test2{
        private final Consumer<String> consumer;

        Test2(final Consumer<String> consumer) {
            this.consumer = consumer;
        }

        public void test(){
            this.consumer.accept(" world");
        }
    }
}

我不明白，在GGGG课上我有String str (状态)

我创建了一个消费者，其方法引用了方法 showElement现在这位消费者引用了GGGGG实例。消费者是否保留对原始对象的引用或创建一个新实例，如果它在被垃圾收集时具有相同的引用？

Answer 1

Java 可与 pass-by-value. 配合使用因此，test2 和 hello 只是引用副本。您仍然保留引用位置的信息。

Does consumer keep a reference to the original object?

是的。

作为附加知识，JLS, Section 15.13.3描述方法引用的运行时评估。

The timing of method reference expression evaluation is more complex than that of lambda expressions (§15.27.4). When a method reference expression has an expression (rather than a type) preceding the :: separator, that subexpression is evaluated immediately. The result of evaluation is stored until the method of the corresponding functional interface type is invoked; at that point, the result is used as the target reference for the invocation. This means the expression preceding the :: separator is evaluated only when the program encounters the method reference expression, and is not re-evaluated on subsequent invocations on the functional interface type.