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This article introduces the knowledge of "what is the Java code block and code loading order". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Local code block

Location: local location (inside the method)

Function: limit the life cycle of variables, release as soon as possible, and save memory

Call: execute when the method it is in is called

Public class partial code block {@ Testpublic void test () {BB = new B (); b.go () }} class B {B () {} public void go () {/ / local code blocks in the method generally make an one-time call, releasing space immediately after the call, so as to avoid occupying stack space in the next call process / / because the stack space memory is limited, method calls may generate a lot of local variables, resulting in insufficient stack memory. / / this can be avoided by using partial code blocks. {int I = 1; ArrayList list = new ArrayList (); while (I

< 1000) { list.add(i ++); } for (Integer j : list) { System.out.println(j); } System.out.println("gogogo"); } System.out.println("hello"); }}构造代码块 位置：类成员的位置，就是类中方法之外的位置 作用：把多个构造方法共同的部分提取出来，共用构造代码块 调用：每次调用构造方法时，都会优先于构造方法执行，也就是每次new一个对象时自动调用，对 对象的初始化 class A{ int i = 1; int initValue;//成员变量的初始化交给代码块来完成 { //代码块的作用体现于此：在调用构造方法之前，用某段代码对成员变量进行初始化。 //而不是在构造方法调用时再进行。一般用于将构造方法的相同部分提取出来。 // for (int i = 0;i < 100;i ++) { initValue += i; } } { System.out.println(initValue); System.out.println(i);//此时会打印1 int i = 2;//代码块里的变量和成员变量不冲突，但会优先使用代码块的变量 System.out.println(i);//此时打印2 //System.out.println(j);//提示非法向后引用，因为此时j的的初始化还没开始。 // } { System.out.println("代码块运行"); } int j = 2; { System.out.println(j); System.out.println(i);//代码块中的变量运行后自动释放，不会影响代码块之外的代码 } A(){ System.out.println("构造方法运行"); }}public class 构造代码块 { @Test public void test() { A a = new A(); }}静态代码块 位置：类成员位置，用static修饰的代码块 作用：对类进行一些初始化 只加载一次，当new多个对象时，只有第一次会调用静态代码块，因为，静态代码块 是属于类的，所有对象共享一份 调用: new 一个对象时自动调用 public class 静态代码块 {@Testpublic void test() { C c1 = new C(); C c2 = new C(); //结果,静态代码块只会调用一次，类的所有对象共享该代码块 //一般用于类的全局信息初始化 //静态代码块调用 //代码块调用 //构造方法调用 //代码块调用 //构造方法调用}}class C{ C(){ System.out.println("构造方法调用"); } { System.out.println("代码块调用"); } static { System.out.println("静态代码块调用"); }} 执行顺序 静态代码块 ----->

Construction code block-> construction method

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