什么是 Java 中的双大括号初始化?

2022-01-18 00:00:00 initialization java double-brace-initialize

什么是 Java 中的双括号初始化语法({{ ... }})?

What is Double Brace initialization syntax ({{ ... }}) in Java?

推荐答案

双大括号初始化创建一个从指定类(外大括号)派生的匿名类，并在该类中提供一个初始化块(内大括号).例如

Double brace initialisation creates an anonymous class derived from the specified class (the outer braces), and provides an initialiser block within that class (the inner braces). e.g.

new ArrayList<Integer>() {{
   add(1);
   add(2);
}};

请注意，使用这种双括号初始化的效果是您正在创建匿名内部类.创建的类有一个指向周围外部类的隐式 this 指针.虽然通常不是问题，但在某些情况下可能会导致悲伤，例如在序列化或垃圾收集时，请注意这一点.

Note that an effect of using this double brace initialisation is that you're creating anonymous inner classes. The created class has an implicit this pointer to the surrounding outer class. Whilst not normally a problem, it can cause grief in some circumstances e.g. when serialising or garbage collecting, and it's worth being aware of this.

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