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 declaration of a class to indicate its base class, the default base class is the Object class, ex:
public class Person{ ~~~~~}Equivalent to
public class Person extends Object{ ~~~~~}2. equals method of Object class
①. The definitions in the Object class are:
public boolean equals(Object obj) method.
Provides logic that defines whether objects are equal.
②. Object'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. Some classes provided by J2SDK, 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 When the attribute contents are equal (not necessarily equal objects), return true otherwise return false.
④. The equals() method can be rewritten 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 ; }}The running results are shown in the figure below:
I hope this article will be helpful to everyone’s Java programming.