Java Interview Question: Difference Between == and equals() in Java (With Examples)

 🔹 Introduction

Understanding the difference between == and equals() is one of the most fundamental Java interview questions.

👉 Interviewers ask this to check your understanding of:

• Memory
• Object comparison
• String handling

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🔹 What is == in Java?

== is used to compare memory references (addresses).

👉 It checks:

• Whether two variables point to the same object

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🔹 Example Using ==

public class Test {
    public static void main(String[] args) {
        String a = new String("hello");
        String b = new String("hello");

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

🔹 Output

false

👉 Because both objects are stored in different memory locations

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🔹 What is equals() in Java?

equals() is used to compare actual content (values).

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🔹 Example Using equals()

public class Test {
    public static void main(String[] args) {
        String a = new String("hello");
        String b = new String("hello");

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

🔹 Output

true

👉 Because values are the same

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🔍 Important Interview Scenario

String x = "java";
String y = "java";

System.out.println(x == y);

🔹 Output

true

👉 Why?

Because of String Constant Pool
Both variables point to same memory

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⚡ Key Differences

Feature	==	equals()
Comparison	Memory reference	Content/value
Used for	Primitives + Objects	Objects only
Overridable	No	Yes

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🔹 When to Use What?

✔ Use ==

• For primitive types
• For reference comparison

✔ Use equals()

• For comparing object values

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🔹 Common Mistake

❌ Using == for String comparison
👉 Leads to wrong results

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🔹 Time Complexity

• O(1) for ==
• O(n) for equals() (depends on object)

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🔹 Key Takeaways

✔ == → compares memory
✔ equals() → compares value
✔ String pool affects behavior
✔ Very frequently asked interview question

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🔹 Conclusion

Understanding == vs equals() is essential for writing correct Java programs and performing well in interviews.

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