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The Java Interview Handbook: 300+ Interview Questions

The Object Class

Explore how the default equals method in Java's Object class compares object references, why it fails for certain cases like Integer or String, and the importance of overriding both equals and hashCode methods. Understand how these methods affect object equality and behavior in hash-based collections, and learn best practices for implementing them correctly.

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1.

What is the Object class?

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Java
class HelloWorld {
    public static void main( String args[] ) {
        System.out.println((new ObjectSubclass()) instanceof Object);      
    }
}
class ObjectSubclass {
}
1.

What are the methods defined in the Object class?

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Technical Quiz
1.

What is the output of the below snippet?

    String obj1 = new String("abc");
    String obj2 = new String("abc");
    System.out.println(obj1 == obj2);
A.

false

B.

true

1 / 4

The equals() method provided in the Object class uses the identity operator == to determine whether two objects are equal. For primitive data types, this gives the correct result. For objects, however, it does not. The equals() method provided by Object tests whether the object references are equal — that is, if the object references are pointing to the same address in memory. This is the reason the statement new Integer(5) == new Integer(5) will output false because the two integer objects have different memory ...