Java Object class usage example

The examples in this article describe the usage of Object class in java. Share it with everyone for your reference. The details are as follows:

1. The Object class is the base class of all java classes.

If the extends keyword is not used in the class declaration to indicate its base class, the default base class is the Object class. ex:

public class Person{
 
　　　　~~~~~
 
}

is equivalent to

public class Person extends Object{
 
　　　　~~~~~
 
}

2, equals method of Object class

①, defined in Object class There are:

public boolean equals(Object obj) method.

Provides logic for defining whether objects are equal.

②, Objec's equals method is defined as: x.equals(y) returns true when x and y are applications of the same object, otherwise returns false.

③, provided by J2SDK Some classes, such as String, Date, etc., override the equals() method of Object, and call the equals method of these classes, x.equals(y), when x and y refer to the same type of object and the attribute contents are equal ( not necessarily equal objects), returns true otherwise returns false.

④. You can override the equals() method in the user-defined type as needed.

The example code is as follows:

public class TestEquals{
  public static void main (String args[]){
    Cat cat1 = new Cat(1,2,3);
    Cat cat2 = new Cat(1,2,3);
    System.out.println(cat1 == cat2);
    System.out.println(cat1.equals(cat2  ));
     
    String s1 = new String("hello");
    String s2 = new String("hello");
    System.out.println(s1 == s2);
    System.out.println(s1.equals(s2));
     
  }
}
class Cat{
  int color;
  int height,weight;
   
  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;
  }
}

I hope this article will be helpful to everyone’s Java programming.

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