Java中的初始化程序块

为了在为实例数据成员赋值时执行任何操作，使用了初始化块。简单来说，初始化块用于声明/初始化类的各种构造函数的公共部分。每次创建对象时它都会运行。

初始化程序块包含在创建实例时始终执行的代码，并且在每次创建类的对象时运行。我们可以在 3 个区域使用初始化程序块：

• 构造函数
• 方法
• 块

Tip: If we want to execute some code once for all objects of a class then we will be using Static Block in Java

示例 1：

Java

// Java Program to Illustrate Initializer Block
  
// Class
class Car {
  
    // Class member variable
    int speed;
    
    // Constructor
    Car()
    {
  
        // Print statement when constructor is called
        System.out.println("Speed of Car: " + speed);
    }
    // Block
    {
        speed = 60;
    }
    // Class member method
    public static void main(String[] args)
    {
  
        Car obj = new Car();
    }
}

输出

Speed of Car: 60

示例 2：

Java

// Java Program to Illustrate Initializer Block
  
// Importing required classes
import java.io.*;
  
// Main class
public class GFG {
  
    // Initializer block starts..
    {
        // This code is executed before every constructor.
        System.out.println(
            "Common part of constructors invoked !!");
    }
    // Initializer block ends
  
    // Constructor 1
    // Default constructor
    public GFG()
    {
  
        // Print statement
        System.out.println("Default Constructor invoked");
    }
  
    // Constructor 2
    // Parameterized constructor
    public GFG(int x)
    {
  
        // Print statement
        System.out.println(
            "Parameterized constructor invoked");
    }
  
    // Main driver method
    public static void main(String arr[])
    {
  
        // Creating variables of class type
        GFG obj1, obj2;
  
        // Now these variables are
        // made to object and interpreted by compiler
        obj1 = new GFG();
  
        obj2 = new GFG(0);
    }
}

输出

Common part of constructors invoked !!
Default Constructor invoked
Common part of constructors invoked !!
Parameterized constructor invoked

Note: The contents of the initializer block are executed whenever any constructor is invoked (before the constructor’s contents)
The order of initialization constructors and initializer block doesn’t matter, the initializer block is always executed before the constructor.

有关Java中的实例初始化的更多详细信息，请参阅文章Java中的实例初始化块 (IIB)