August 28th 2018

Difference between == and equals method is not one of the most frequently asked question in java developer interview. We need to understand the concept of equals() method and == operator in java.

What is == operator ?

To compare primitives and objects we use "==" equality operator in java which is a binary operator given in the java programming language.
a. If we are comparing primitives ,== operator works fine, but if we compare objects then it creates confusion with equals() method in java. "==" operator compares two object based on memory reference.

What is equals() method in java?

Two objects are considered equal if they have the same states (values). equals() method is present in the Object class.You need to override the hashCode() method if you override the equals() method so as not to break the contract. As per the API, hashCode() method for two objects should return the same value if their equals method show that they are equivalent. Vice - versa may not be true.

Difference between == and equals method in java

1. Primitives or Objects : == operator is used to compare primitives while equals() method is used to check equality of objects.

2. Comparison : == compares two objects based on memory reference. equals method compares based on the values.

3. Type : == is a binary operator, while equals() is a method.

String and Integer example of == and equals() method
Most of the time, programmers should use "equals()" rather than "==" to avoid unexpected outcome. It simply because ".equals" will compare 2 strings character by character to determine equality while "==" checks whether 2 string objects are identical. Try to do this experiment and you will understand:

String a = new String ("a");

String b = new String ("a");

System.out.println (a == b);

Outcome : false

String a = new String ("a");

String b = new String ("a");

System.out.println (a.equals(b));

Outcome : true

Two strings are equal in case of equals method if both strings that you are comparing have the same characters and have the same case such as
"hello".equals("hello") will return true
as both the strings have the same characters h,e,l,l,o and they do have the same length and also have the same case.
Now change the case of h to H i.e write "Hello".equals("hello") this will return false which shows that the strings are not equal.

In other words ,

Example 1:

Integer i = new Integer(10);
Integer j = i;

in the above code, i == j is true because both i and j refer to the same object.

Example 2:

Integer i = new Integer(10);
Integer j = new Integer(10);

In the above code, i == j is false because, although they both have the value 10, they are two different objects.

That's it for today, please mention in comments if you have any questions regarding difference between == and equals() method in java.

This post first appeared on Java Hungry, please read the originial post: here

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