这篇文章主要介绍了Java静态和非静态成员变量初始化过程解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
这篇文章主要介绍了Java静态和非静态成员变量初始化过程解析,文中通过示例代码介绍的非常详细，对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下
Java中非静态成员变量、静态成员变量的初始化时机。
非静态变量
我们在这里分析三种结构，着重分析这三种结构的初始化顺序：
成员变量初始化语句；
成员变量初始化块；
构造函数；
示例一：
public class MyTest { private String name = "wei.hu"; public MyTest(String name) { System.out.println("This is constructor. Will assign the variable name to: " + name + "."); System.out.println("Before the name was modified: " + this.name); this.name = name; System.out.println("After the name was modified: " + this.name); } { System.out.println("This is initialize block. Will assign the variable name to: chouchou"); System.out.println("Before the name was modified: " + this.name); this.name = "chouchou"; System.out.println("After the name was modified: " + this.name); } public String getName() { return name; } public static void main(String[] args) { MyTest myTest = new MyTest("mengna"); System.out.println(myTest.getName()); } } #输出 This is initialize block. Will assign the variable name to: chouchou Before the name was modified: wei.hu After the name was modified: chouchou This is constructor. Will assign the variable name to: mengna. Before the name was modified: chouchou After the name was modified: mengna mengna
示例二：
public class MyTest { public MyTest(String name) { System.out.println("This is constructor. Will assign the variable name to: " + name + "."); System.out.println("Before the name was modified: " + this.name); this.name = name; System.out.println("After the name was modified: " + this.name); } private String name = "wei.hu"; { System.out.println("This is initialize block. Will assign the variable name to: chouchou"); System.out.println("Before the name was modified: " + this.name); this.name = "chouchou"; System.out.println("After the name was modified: " + this.name); } public String getName() { return name; } public static void main(String[] args) { MyTest myTest = new MyTest("mengna"); System.out.println(myTest.getName()); } } #结果（与示例一相同） This is initialize block. Will assign the variable name to: chouchou Before the name was modified: wei.hu After the name was modified: chouchou This is constructor. Will assign the variable name to: mengna. Before the name was modified: chouchou After the name was modified: mengna mengna
示例三：
public class MyTest { public MyTest(String name) { System.out.println("This is constructor. Will assign the variable name to: " + name + "."); System.out.println("Before the name was modified: " + this.name); this.name = name; System.out.println("After the name was modified: " + this.name); } { System.out.println("This is initialize block. Will assign the variable name to: chouchou"); System.out.println("Before the name was modified: " + this.name); this.name = "chouchou"; System.out.println("After the name was modified: " + this.name); } private String name = "wei.hu"; public String getName() { return name; } public static void main(String[] args) { MyTest myTest = new MyTest("mengna"); System.out.println(myTest.getName()); } } #结果 This is initialize block. Will assign the variable name to: chouchou Before the name was modified: null After the name was modified: chouchou This is constructor. Will assign the variable name to: mengna. Before the name was modified: wei.hu After the name was modified: mengna mengna 分析： 注意本示例的结果与上面两个示例的结果不同。 1、当我们想将成员变量name赋值为chouchou之前，发现this.name为null。也就是说初始化语句没有先执行，而是先执行了初始化块； 2、当在执行构造函数时，我们想将成员变量name赋值为mengna，发现赋值之前，this.name不再是chouchou，而是wei.hu，这说明了什么？ 因为初始化块先执行，如果紧接着执行构造函数的话，那么在构造函数赋值语句执行之前，this.name应该是chouchou才对。但是在构造函数赋值语句执行之前，this.name的值变成了wei.hu，那么足以证明： 1）初始化块先执行； 2）下来执行了初始化语句； 3）最后执行了构造函数；
结论：
通过上面三个示例，我们可以发现，对于非静态的成员变量：
初始化语句、初始化块，总是先于构造函数执行；
初始化语句、初始化块的和执行顺序，取决于 初始化语句、初始化块在代码中的书写顺序。写在上面的先执行。
静态变量
我们在这里也分析三种结构：
静态初始化语句；
静态初始化块；
构造函数；
示例一：
public class MyTest { public static String name = "wei.hu"; public Mytest() { System.out.println("This is constructor. Will assign the variable name to: chouchou"); System.out.println("Before the name was modified: " + name); name = "chouchou"; System.out.println("After the name was modified: " + name); } static { System.out.println("This is static initialize block. Will assign the variable name to: mengna"); System.out.println("Before the name was modified: " + name); name = "mengna"; System.out.println("After the name was modified: " + name); } public static void main(String[] args) { System.out.println(MyTest.name); } } #结果 This is static initialize block. Will assign the variable name to: mengna Before the name was modified: wei.hu After the name was modified: mengna mengna 分析： 通过打印输出，我们发现在执行静态初始快之前，静态变量name已经初始化为wei.hu了。也就是说： 1、静态初始化语句先执行； 2、下来执行静态初始化块； 3、构造函数未执行； ---------------------
示例二：
public class MyTest { public Mytest() { System.out.println("This is constructor. Will assign the variable name to: chouchou"); System.out.println("Before the name was modified: " + MyTest.name); name = "chouchou"; System.out.println("After the name was modified: " + MyTest.name); } static { System.out.println("This is static initialize block. Will assign the variable name to: mengna"); System.out.println("Before the name was modified: " + MyTest.name); name = "mengna"; System.out.println("After the name was modified: " + MyTest.name); } public static String name = "wei.hu"; public static void main(String[] args) { System.out.println(MyTest.name); } } #结果 This is static initialize block. Will assign the variable name to: mengna Before the name was modified: null After the name was modified: mengna wei.hu 分析： 初始化块在对静态变量赋值之前，发现MyTest.name的值为空。 在最后打印出MyTest.name时，发现输出的值是wei.hu，而不是mengna。也就是说，在初始化块执行之后，执行了静态初始化语句。 1、先执行静态初始化块； 2、再执行静态初始化语句； 3、构造函数未执行； ---------------------
结论：
对于静态字段，初始化有如下规则：
1. 若静态初始化语句在前，静态代码块在后，则先执行静态初始化语句；
2. 若静态代码块在前，静态初始化语句在后，则先执行静态代码块；
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