Java Lambda : How it works in JVM & is it OOP?

Question

例如，在匿名内部类的情况下，传递(匿名)对象引用并执行该对象的方法。

Lambda 是在需要时执行的代码块。

当遇到 lambda 时，JVM 会发生什么？ JVM 将 lambdas 相关的代码块存放在哪里(Heap : Young, Old or Permanent Generation)？

我尝试搜索，我得到了使用 lambdas 的语法，但无法理解 JVM 内部发生了什么，因为在 JAVA 中一切都是基于对象的。

1. 那么在 OOP 的上下文中，lambda 是如何工作的？

2. lambda 是否违反 OOP 概念？

3. Lambda 对垃圾收集器有好处吗，因为没有创建对象 不用担心内存问题和清​​除内存？

Answer 1

我不会浪费时间去思考 lambda 表达式是否违反了 OO 原则。它的目标是增加语言的能力，而不是编写 OO 代码，我看不出 lambdas 是如何违反封装、继承或多态性的。

这个 article解释 Java 如何处理 lambda 表达式:

What’s interesting about Lambda expressions is that from the JVM’s perspective they’re completely invisible. It has no notion of what an anonymous function or a Lambda expression is. It only knows bytecode which is a strict OO specification. It’s up to the makers of the language and its compiler to work within these constraints to create newer, more advanced language elements.

考虑以下代码:

List names = Arrays.asList("1", "2", "3");
Stream lengths = names.stream().map(name -> name.length());

... It begins quite simply by loading the names var and invokes its .stream() method, but then it does something quite elegant. Instead of creating a new object that will wrap the Lambda function, it uses the new invokeDynamic instruction which was added in Java 7 to dynamically link this call site to the actual Lambda function.

aload_1 //load the names var

// call its stream() func
invokeinterface java/util/List.stream:()Ljava/util/stream/Stream;

//invokeDynamic magic!
invokedynamic #0:apply:()Ljava/util/function/Function;

//call the map() func
invokeinterface java/util/stream/Stream.map:
(Ljava/util/function/Function;)Ljava/util/stream/Stream;

InvokeDynamic is an instruction that was added in Java 7 to make the JVM less strict, and allows dynamic languages to bind symbols at run-time, vs. doing all the linkage statically when the code is compiled by the JVM.

Lambda 代码

aload_0
invokevirtual java/lang/String.length:()
invokestatic java/lang/Integer.valueOf:(I)Ljava/lang/Integer;
areturn