String中equals方法

Java中使用“==”来判断两个对象是否相等是判断两个对象的引用是否相同
Java中使用“equals”来判断两个对象是否相等默认是判断两个对象的引用是否相同，然而还需看对象的equals方法是否被重写。一般来说，Java中String的equals被重写了，判断的是两个String对象字符串级别是否相同。

    package Chapter03;
    
    class Cat3{
        
        int height, weight;
        
        Cat3(int height, int weight){
            this.height = height;
            this.weight = weight;
        }
        
        public boolean equals(Object obj){
            if (obj instanceof Cat3){
                Cat3 c = (Cat3) obj;
                if (c.height == this.height && c.weight == this.weight){
                    return true;
                }
                
            }
            return false;
        }
    }
    
    
    public class equalsDemo {
    
        /**
         * @param args
         */
        public static void main(String[] args) {
            // TODO Auto-generated method stub
            
            Cat3 c1 = new Cat3(5, 10);
            Cat3 c2 = new Cat3(5, 10);
            System.out.println(c1==c2);
            System.out.println(c1.equals(c2));
            String s1 = new String("hello");   # false
            String s2 = new String("hello");   # true
            System.out.println(s1==s2);   # false
            System.out.println(s1.equals(s2));   # true
        }
    
    }