Difference between comparing String using == and .equals() method in Java
Both equals() method and the == operator are used to compare two objects in Java. == is an operator and equals() is method. But == operator compares reference or memory location of objects in a heap, whether they point to the same location or not.
Whenever we create an object using the operator new, it will create a new memory location for that object. So we use the == operator to check memory location or address of two objects are the same or not.
In general, both equals() and “==” operators in Java are used to compare objects to check equality, but here are some of the differences between the two:
- The main difference between the .equals() method and == operator is that one is a method, and the other is the operator.
- We can use == operators for reference comparison (address comparison) and .equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas .equals() evaluates to the comparison of values in the objects.
- If a class does not override the equals method, then by default, it uses the equals(Object o) method of the closest parent class that has overridden this method. See Why to Override equals(Object) and hashCode() method ? in detail.
true false true true
Explanation: Here, we create two objects, namely s1 and s2.
- Both s1 and s2 refer to same objects.
- When we use the == operator for s1 and s2 comparison, the result is true as both have the same addresses in the string constant pool.
- Using equals, the result is true because it’s only comparing the values given in s1 and s2.
Java String Pool
|s1 = “HELLO”|
s2 = “HELLO”
|s3 = “HELLO”|
Let us understand both the operators in detail:
We can apply equality operators for every primitive type, including the boolean type. We can also apply equality operators for object types.
false false true true
If we apply == for object types then, there should be compatibility between arguments types (either child to parent or parent to child or same type). Otherwise, we will get a compile-time error.
false false // error: incomparable types: Thread and String
In Java, the String equals() method compares the two given strings based on the data/content of the string. If all the contents of both the strings are the same, it returns true. If all characters are not matched, then it returns false.
true false false false true
Explanation: Here, we are using the .equals method to check whether two objects contain the same data or not.
- In the above example, we create 3 Thread objects and 2 String objects.
- In the first comparison, we check whether t1 == t3 or not. As we know that both t1 and t3 point to the same object. That’s why it returns true.
- In the second comparison, we are using the operator “==” for comparing the String Objects and not the contents of the objects. Here, both the objects are different, and hence the outcome of this comparison is “False.”
- When we are comparing 2 String objects by .equals() operator, then we are checking that is both objects contain the same data or not.
- Both the objects contain the same String, i.e., GEEKS. That’s why it returns true.
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