10 Tricky Java Interview Questions and Their Answers Explained

Q1: What is the output of the following Java code?

public class Test {
  public static void main(String[] args) {
    method(null);
  }

  public static void method(Object o) {
    System.out.println("Object method");
  }

  public static void method(String s) {
    System.out.println("String method");
  }
}

Answer: It prints "String method". The compiler selects the most specific overload, and method(String s) is more specific than method(Object o).

Q2: What is the output of the following Java code?

public class Test {
  public static void main(String[] args) {
    Integer num1 = 100;
    Integer num2 = 100;
    if (num1 == num2) {
      System.out.println("num1 == num2");
    } else {
      System.out.println("num1 != num2");
    }
  }
}

Answer: It prints "num1 == num2". Because Integer values between -128 and 127 are cached, the two references point to the same object, making the == comparison true.

Q3: How does garbage collection prevent a Java application from running out of memory?

Answer: The Java garbage collector does not guarantee that an application will never run out of memory; it only reclaims memory occupied by objects that are no longer reachable.

Q4: Is Java "pass‑by‑reference" or "pass‑by‑value"?

Answer: Java is always pass‑by‑value. When a reference type is passed, the value being passed is the reference itself, not the actual object.

Q5: How many String objects are created by the following code?

public class Test {
  public static void main(String[] args) {
    String s = new String("Hello World");
  }
}

Answer: Two String objects are created: one in the heap (the explicit new String) and one in the string‑constant pool for the literal "Hello World".

Q6: What is the output of the following code?

public class Test {
  public static void main(String[] arr) {
    System.out.println(0.1 * 3 == 0.3);
    System.out.println(0.1 * 2 == 0.2);
  }
}

Answer: The first print outputs false, the second outputs true. The discrepancy is due to binary floating‑point rounding errors.

Q7: Can a static method be overridden or overloaded in Java?

Answer: Static methods can be overloaded but not overridden. Declaring a static method with the same signature in a subclass hides the superclass method rather than overriding it.

Q8: What is the most reliable way to test equality of two double values?

Answer: Use Double.compare(d1, d2) == 0.

Q9: If a try or catch block executes a return statement, does the finally block still run?

Answer: Yes, the finally block always runs unless the JVM exits via System.exit().

Q10: What is the output of the following code?

public class Test {
  public static void main(String[] args) {
    System.out.println("main method");
  }

  public static void main(String args) {
    System.out.println("Overloaded main method");
  }
}

Answer: It prints "main method". The overloaded main method is not invoked automatically; it would need to be called explicitly from the standard main.