利用两种方式分别实现单例模式（懒汉式、饿汉式）

package testsingle;
    //实现单例的两种方式
public class TestMySingle {
    public static void main(String[] args) {
        ClassA ca1 = ClassA.getClassA();
        ClassA ca2 = ClassA.getClassA();
        System.out.println(ca1==ca2);
        ClassB cb1 = ClassB.getClassB();
        ClassB cb2 = ClassB.getClassB();
        System.out.println(cb1==cb2);
    }
}
class ClassA{       //饿汉式
    private static final ClassA ca = new ClassA();
    private ClassA(){}
    public static ClassA getClassA(){
        return ca;
    }
}
class ClassB{       //懒汉式
    private static  ClassB cb ;
    private ClassB(){}
    public synchronized static ClassB getClassB(){
        if(cb==null){
            cb = new ClassB();
        }
        return cb;
    }
}