类的同时初始化

同时初始化两个类的意义在于当两个类之间关系密切，即方法经常与另一个类进行通信时，可以简化通信

/**
 * 同时初始化只适用于单例模式，且不适用于饿汉式 
 */
class A {
	public static A a;
	private String name = "A";
	
	public static A getInstance() {
		if(a==null)
		{
			a = new A();
			//初始化B
			B.getInstance();
		}
		return a;
	}
	
	@Override
	public String toString() {
		return name;
	}
}

class B {
	public static B b;
	private String name = "B";
	
	public static B getInstance() {
		if(b==null)
		{
			b = new B();
			//初始化C
			C.getInstance();
		}
		return b;
	}
	
	@Override
	public String toString() {
		return name;
	}
}

class C {
	public static C c;
	private String name = "C";
	
	public static C getInstance() {
		if(c==null)
		{
			c = new C();
			//初始化A
			A.getInstance();
		}
		return c;
	}
	
	@Override
	public String toString() {
		return name;
	}
}

public class Test {
	public static void main(String[] args) {
		//未初始化
		System.out.println(A.a+" "+B.b+" "+C.c);
		//同时初始化
		A.getInstance();
		System.out.println("Hello, world!");
		System.out.println(A.a+" "+B.b+" "+C.c);
	}
}