java核心技术——静态初始化块

最新推荐文章于 2023-09-09 10:05:18 发布

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本文深入解析静态初始化块在Java中的作用及使用场景，强调其在类加载时仅执行一次的特性，以及如何利用它为静态变量赋初值。通过具体代码示例，展示了静态初始化块与普通对象初始化块的区别。

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静态初始化块只在类加载时执行，且只会执行一次，同时静态初始化块只能给静态变量赋值，不能初始化普通的成员变量。

import java.util.Random;

public class ConstructorTest 
{
	
	public static void main(String[] args) 
	{
		//fill the staff array with three Employee objects
		Employee01[] staff = new Employee01[3];
		staff[0] = new Employee01("周杰伦", 40000);
		staff[1] = new Employee01(60000);
		staff[2] = new Employee01();
		
		for(Employee01 e : staff)
		{
			System.out.println("名字：" + e.getName() + ", id = " + e.getId() + ", 薪水：" + e.getSalary());
		}	
	}	
}

class Employee01{
	private static int nextId;
	
	private int id;
	private String name = "";  //instance field initialization
	private double salary;
	
	
	// static initialization block  静态初始化块
	static  //静态初始化块只在类加载时执行，且只会执行一次，同时静态初始化块只能给静态变量赋值，不能初始化普通的成员变量。
	{
		Random generator = new Random();
		//set nextId to a random number between 0 and 9999
		nextId = generator.nextInt(10000);
	}
	// object initialization block	初始化对象块
	{
		id = nextId;
		nextId++;
		salary = 100;
	}
	
	// three overload constructor  三个重载构造器
	public Employee01(String name, double salary)
	{
		this.name = name;
		this.salary = salary;
	}
	public Employee01(double salary)
	{
		this("Employee" + nextId, salary);
	}
	
	public Employee01()
	{
		
	}
	public int getId() 
	{
		return id;
	}

	public String getName() 
	{
		return name;
	}

	public double getSalary()
	{
		return salary;
	}	
}

名字：周杰伦, id = 6020, 薪水：40000.0
名字：Employee6021, id = 6021, 薪水：60000.0
名字：, id = 6022, 薪水：100.0