Difference between comparing String using == and .equals() method in Java

In Java, there is a difference between comparing strings using the == operator and the .equals() method.

We have to use the "==" operator to compare strings only when you want to check if two string variables refer to the exact same memory location. If you want to compare the contents of two strings, you should use the .equals() method to ensure accurate comparison.

The == operator

The == operator compares the object references of two strings, not their actual contents. It checks if the two string references point to the same memory location. In other words, it checks if the two string objects are exactly the same object in memory.

For example:

FileName: StringComparisonExample.java

Here the given Java program demonstrates the use of the == operator for string comparison, Integer Comparison and Object Comparison.

public class StringComparisonExample {
 public static void main(String[] args) {
 // String comparison
 String str1 = "Hello";
 String str2 = "Hello";
 String str3 = new String("Hello");
 System.out.println("Comparing using == operator:");
 System.out.println("str1 == str2: " + (str1 == str2)); // Comparing string literals
 System.out.println("str1 == str3: " + (str1 == str3)); // Comparing string literal with a new string object
 // Integer comparison
 int num1 = 10;
 int num2 = 10;
 System.out.println("\nComparing using == operator:");
 System.out.println("num1 == num2: " + (num1 == num2)); // Comparing integer variables
 // Object comparison
 Integer obj1 = new Integer(5);
 Integer obj2 = new Integer(5);
 System.out.println("\nComparing Integer objects using == operator:");
 System.out.println("obj1 == obj2: " + (obj1 == obj2)); // Comparing Integer objects using the == operator
 }
}

Output

Comparing using == operator:str1 == str2: true
str1 == str3: false
Comparing using == operator:
num1 == num2: true
Comparing Integer objects using == operator:
obj1 == obj2: false

The .equals() Method

In Java, the .equals() method compares the actual content of two strings. It checks if the characters inside the strings are the same.

Example 2

In this java program, we have two scenarios for using the .equals() method:

1. String comparison: We have three strings, str1, str2, and str3. We use the .equals() method to compare str1 with str2 and str1 with str3.
2. Object comparison: We create two Integer objects, obj1 and obj2, both with a value of 5. We use the .equals() method to compare them.

FileName: StringEqualsExample.java

public class StringEqualsExample {
 public static void main(String[] args) {
 // String comparison
 String str1 = "Hello";
 String str2 = "Hello";
 String str3 = new String("Hello");
 System.out.println("Comparing using .equals() method:");
 System.out.println("str1.equals(str2): " + str1.equals(str2));
 System.out.println("str1.equals(str3): " + str1.equals(str3));
 // Object comparison
 Integer obj1 = new Integer(5);
 Integer obj2 = new Integer(5);
 System.out.println("\nComparing Integer objects using .equals() method:");
 System.out.println("obj1.equals(obj2): " + obj1.equals(obj2));
 }
}

Output

Comparing using .equals() method:str1.equals(str2): true
str1.equals(str3): true
Comparing Integer objects using .equals() method:
obj1.equals(obj2): true

Example 3

In the given java program as you can see, the == operator correctly compares the references of the string objects, while the .equals() method compares the actual string contents to determine equality.

FileaName: ComparisonExample.java

public class ComparisonExample {
 public static void main(String[] args) {
 String str1 = "Hello";
 String str2 = "Hello";
 String str3 = new String("Hello");
 // String comparison using == operator
 System.out.println("String comparison using the == operator:");
 System.out.println(str1 == str2); // true
 System.out.println(str1 == str3); // false
 // String comparison using .equals() method
 System.out.println("\nString comparison using the .equals() method:");
 System.out.println(str1.equals(str2)); // true
 System.out.println(str1.equals(str3)); // true
 // Object comparison using == operator
 System.out.println("\nObject comparison using the == operator:");
 Object obj1 = new Object();
 Object obj2 = new Object();
 Object obj3 = obj1;
 System.out.println(obj1 == obj2); // false
 System.out.println(obj1 == obj3); // true
 // Object comparison using .equals() method
 System.out.println("\nObject comparison using the .equals() method:");
 System.out.println(obj1.equals(obj2)); // false
 System.out.println(obj1.equals(obj3)); // true
 }
}

Output

String comparison using the == operator:
true
false
String comparison using the .equals() method:
true
true
Object comparison using the == operator:
false
true
Object comparison using the .equals() method:
false
true