How to Compare Two Objects in Java

Java Object class is the super class of all the Java classes. All Java classes implements the Object class by default. The Java Object class provides the two important methods to compare two objects in java.

Java provides the two methods of the Object class to compare the objects are as follows:

• Java equals() Method
• Java hashCode() Method

Java equals() Method

The equals() method of the Object class compare the equality of two objects. The two objects will be equal if they share the same memory address.

Java hashCode() Method

It is a unique id provided by jvm to a Java object. Each Java object is associated with the hash code. The hash code is managed by a hash-based data structure.

Remember: When we override the equals() method, it is necessary to override the hashCode() method, also.

Approach: Using equals()

Java

public class CompareTwoObject {
    public static void main(String[] args) {
        Integer num1 = 123;
        Long num2 = 123l;
        System.out.println("Compare two object using equals() " + num1.equals(num2));
        System.out.println("Compare two object using equals() " + num1.equals(123));
        System.out.println("Compare two object using equals() " + num2.equals(123));
        System.out.println("Compare two object using equals() " + num2.equals(123l));
    }
}

Output:

Compare two object using equals() false
Compare two object using equals() true
Compare two object using equals() false
Compare two object using equals() true

Approach: Using hashcode()

Java

public class CompareTwoObject {
    public static void main(String[] args) {
        Person p1=new Person("Ram",25);
        Person p2=new Person("Ram Singh",25);
        Person p3=new Person("Ram",25);
        System.out.println("Hashbode() of p1 "+p1.hashCode());
        System.out.println("Hashbode() of p2 "+p2.hashCode());
        System.out.println("Hashbode() of p3 "+p3.hashCode());
        System.out.println("Compare the p1 and p2 "+p1.equals(p2));
        System.out.println("Compare the p1 and p3 "+p1.equals(p3));
    }
}

class Person {

    private String name;
    private int age;

    
    public Person(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + age;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Person other = (Person) obj;
        if (age != other.age)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

}

Output:

Hashbode() of p1 83654
Hashbode() of p2 -1683822657
Hashbode() of p3 83654
Compare the p1 and p2 false
Compare the p1 and p3 true