甲静块是代码使用静态关键字的块。通常,这些用于初始化静态成员。JVM在类加载时在main方法之前执行静态块。
public class MyClass { static{ System.out.println("Hello this is a static block"); } public static void main(String args[]){ System.out.println("This is main method"); } }
输出结果
Hello this is a static block This is main method
类似于静态块,Java还提供了实例初始化块,用于初始化实例变量,以替代构造函数。
每当您定义初始化块时,Java都会将其代码复制到构造函数。因此,您也可以使用它们在类的构造函数之间共享代码。
public class Student { String name; int age; { name = "Krishna"; age = 25; } public static void main(String args[]){ Student std = new Student(); System.out.println(std.age); System.out.println(std.name); } }
输出结果
25 Krishna
在一个类中,您还可以具有多个初始化块。
public class Student { String name; int age; { name = "Krishna"; age = 25; } { System.out.println("Initialization block"); } public static void main(String args[]){ Student std = new Student(); System.out.println(std.age); System.out.println(std.name); } }
输出结果
Initialization block 25 Krishna
您还可以在父类中定义实例初始化块。
public class Student extends Demo { String name; int age; { System.out.println("Initialization block of the sub class"); name = "Krishna"; age = 25; } public static void main(String args[]){ Student std = new Student(); System.out.println(std.age); System.out.println(std.name); } }
输出结果
Initialization block of the super class Initialization block of the sub class 25 Krishna