String compare

有些对象重写了Object.equals() 方法 String,Date,Byte,Integer,Short,Character,Long,Float,Double,Boolean 

public class Student {

    public static void main(String[] args) {

        String s1 = new String("123");
        String s2 = new String("123");
        String s3 = "123";
        String s4 = "123";
        
        System.out.println(s1 == s2); //false
        System.out.println(s1.equals(s2));  //true
        
        System.out.println(s3 == s4); //true
        System.out.println(s3.equals(s4)); //true
    }
}