Java-20, equals object class of the method

equals method

• Object class definition has:
  • public boolean equals(Object obj)方法
    • Provide a definition object "is equal to" logic
  • Equals method of Object is defined as: x.equals (y) when x and y are the application returns true or false otherwise the same object
  • J2SDK classes offered, such as String, Date, etc., override the equals method of Object, equals method call these classes, of x.equals (y), x and y when the object is referenced by the same type, and attributes of the content is equal to when (not necessarily of the same object) returns true or false otherwise
  • Equals method can be overridden in the user-defined types as needed.

Example:

package com.nyist;

public class TestEquals {
    public static void main(String[] args) {
        Cat c1 = new Cat(1,2,3);
        Cat c2 = new Cat(1,2,3);
        System.out.println(c1 == c2);

　　　　　System.out.println(c1.equals(c2));

　　　　
    }
}

class Cat{
    int color;
    int height,weight;
    
    public Cat(int color,int height,int weight) {
        this.color = color;
        this.height = height;
        this.weight = weight;
    }
}

result:

false 
false

The default implementation of equals method and == is the same, whether the comparison is all the same references.

 

By rewriting can be achieved only compare whether two objects essence is the same.

Example:

package com.nyist;

public class TestEquals {
    public static void main(String[] args) {
        Cat c1 = new Cat(1,2,3);
        Cat c2 = new Cat(1,2,3);
        System.out.println(c1.equals(c2));
    }
}

class Cat{
    int color;
    int height,weight;
    
    public Cat(int color,int height,int weight) {
        this.color = color;
        this.height = height;
        this.weight = weight;
    }
    
    public boolean equals(Object obj){
        if(obj == null)
            return false;
        else {
            if(obj instanceof Cat) {
                Cat c = (Cat)obj;
                if(c.color == this.color && c.height ==this.height && c.weight == this.weight)
                    return true;
            }
        }
        return false;
    }
}

result:

true