静态初始化器vs实例初始化器vs构造函数 [英] Static Initializers vs Instance Initializers vs Constructors

问题描述

我正在攻读Java考试。在我学习的时候，我遇到了对我不熟悉的java语法。例如花括号（{}）隐藏没有名称的类主体，有些有一个static关键字。我发现他们被称为初始化器。任何人都可以帮助我指出他们之间的关键差异，以及它们如何与构造函数不同。感谢

I am studying for an exam about Java. While I was studying, I have encountered syntaxes in java which are unfamiliar to me. Such as a curly braces({}) unside a class body without a name, some has a static keyword. I have found out that they are called "Initializers". Can anyone help me point out key differences among them and how they differ from a Constructor. Thanks

推荐答案

它们之间的主要区别是它们执行的顺序。为了说明，我将用一个例子解释它们：

The main difference between them is the order they are executed. To illustrate, I will explain them with an example:

public class SomeTest {

    static int staticVariable;
    int instanceVariable;        

    // Static initialization block:
    static {
        System.out.println("Static initialization.");
        staticVariable = 5;
    }

    // Instance initialization block:
    {
        System.out.println("Instance initialization.");
        instanceVariable = 10;
    }

    // Constructor
    public SomeTest() {
        System.out.println("Constructor executed.");
    }

    public static void main(String[] args) {
        new SomeTest();
        new SomeTest();
    }
}

输出将是：

Static initalization.
Instance initialization.
Constructor executed.
Instance initialization.
Constructor executed.

简要说明：

$ b $

• 每次实例化对象时，实例初始化块都会在构造函数之前运行。


• 构造函数（显然）在每次实例化对象时运行。

• Static initialization blocks run once the class is loaded by the JVM.
• Instance initialization blocks run before the constructor each time you instantiate an object.
• Constructor (obviously) run each time you instantiate an object.

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