1. Difference between equality operator and equals method
- It’s one of frequently asked interview questions in java.
- We will look into the important differences, with the help of examples.
- We will go through the basics of equality operator and equals method.
- We will summarize the difference between equality operator and equals method.
2. Equality or == operator in java
- Equality operator is mostly used to compare primitives like int, boolean, char etc.
- e.g. 5 == 6 ? true or false ?
- e.g. ‘a’ == ‘A’ ? true or false?
- Equality operator can be used to compare two objects.
- The two objects will be equals if they same.
- e.g.
- Object obj1 = new Object()
- Object obj3 = obj1
- obj1 & obj3 are equals because both are pointing to same “new Object()”.
- The objects will be equals if they have same references like obj3 & obj1.
- The two objects will be equals if they same.
3. Code: equality (or ==) operator to compare primitives
package org.learn;public class ComparePrimitivesEqualityOperator { public static void main(String[] args) { boolean result; //Example 1: int int10 = 10; int int20 = 20; int anotherInt10 = 10; //Output: result = false result = (int10 == int20); System.out.printf("1. Result of %d == %d is %b",int10,int20,result); //Output: result = true result = (int10 == anotherInt10); System.out.printf("\n1.1. Result of %d == %d is %b",int10,anotherInt10,result); //Example 2: int char_a = 'a'; int char_b = 'b'; int char_A = 'A'; //Output: result = false; result = (char_a == char_b); System.out.printf("\n2. Result of %c == %c is %b",char_a,char_b,result); //Output: result = false; result = (char_a == char_A); System.out.printf("\n2.1. Result of %c == %c is %b",char_a,char_A,result); }} |
4. Output – equality (or ==) operator to compare primitives in java.
1. Result of 10 == 20 is false1.1. Result of 10 == 10 is true2. Result of a == b is false2.1. Result of a == A is false |
5. Program – equality (or ==) operator to compare objects in java.
package org.learn;public class CompareObjectsEqualityOperator { public static void main(String[] args) { //Example 1: //obj1 points to unique memory address in heap store Object obj1 = new Object(); //obj2 points to unique memory address in heap store Object obj2 = new Object(); //obj3 and obj1 points to same memory address Object obj3 = obj1; //Output: Obj1 and Obj2 are not equals if(obj1 == obj2) { System.out.println("1. Obj1 and Obj2 are equals"); } else { System.out.println("1. Obj1 and Obj2 are not equals"); } //Output: Obj1 and Obj3 are equals if(obj1 == obj3) { System.out.println("2. Obj1 and Obj3 are equals"); } else { System.out.println("2. Obj1 and Obj3 are not equals"); } //Example 2: String str1 = new String("USA"); String str2 = new String("USA"); //Output: str1 and str2 are not equals if(str1 == str2) { System.out.println("3. str1 and str2 are equals"); } else { System.out.println("3. str1 and str2 are not equals"); } }} |
6. Output – equality (or ==) operator to compare objects in java.
1. Obj1 and Obj2 are not equals2. Obj1 and Obj3 are equals3. str1 and str2 are not equals |
7. Equals method in java
- equals method is defined in the Object class.
- The equals method of Object class, check whether two objects are equals.
- The Object class implementation of equals method is same as equality operator (to compare objects).
- Object obj1 = new Object();
- Object obj2 = obj1;
- obj1.equals(obj2) will returns true
-
publicbooleanequals(Object obj) {return(this== obj);}
- The concrete classes overrides, the equals method of Object class.
- e.g. String class override equals method to compare contents of String.
- String str1 = new String(“USA”);
- String str2 = new String(“USA”);
- str1.equals(str2) will returns true
- e.g. String class override equals method to compare contents of String.
- Generally concrete classes like String etc., override equals method, to compare the contents.
- So, the behavior of equals method, depends upon the implementation, in concrete class.
8. Program – equals method to compare two objects in java
package org.learn;public class ComparePrimitivesEqualityOperator { public static void main(String[] args) { boolean result; //Example 1: int int10 = 10; int int20 = 20; int anotherInt10 = 10; //Output: result = false result = (int10 == int20); System.out.printf("1. Result of %d == %d is %b",int10,int20,result); //Output: result = true result = (int10 == anotherInt10); System.out.printf("\n1.1. Result of %d == %d is %b",int10,anotherInt10,result); //Example 2: int char_a = 'a'; int char_b = 'b'; int char_A = 'A'; //Output: result = false; result = (char_a == char_b); System.out.printf("\n2. Result of %c == %c is %b",char_a,char_b,result); //Output: result = false; result = (char_a == char_A); System.out.printf("\n2.1. Result of %c == %c is %b",char_a,char_A,result); }} |
9. Output – equals method to compare two objects in java.
1. Obj1 and obj2 are equals2. Contents of str1 and str2 are equals |
10. Difference between equality operator and equals method in java
- Equality operator is mostly used to compare primitives (Refer Section 1).
- What will happens when equality operator compare objects?
- The comparison operator will return true, when same objects are compared.
- What will happens when equality operator compare objects?
- Equals method is generally used to compare the contents.
- e.g. equals method of String class, compares the content of two String.
- The behavior of equals method is dependent, upon the implementation in concrete class.