The ultimate guide to Java interviews with 300+ real-world questions and answers. Get interview-ready in just a few hours with strategies developed by FAANG engineers.

It’s very common to have interviews testing your knowledge of a programming language you claim to be an expert in.

If you've got an interview coming up on Java soon and need to get up to speed, this is the ideal course for you. You'll refresh your memory on everything from the basics to more advanced functionality you’re likely to be asked about. Even if you're using Java every day, you may not have been exposed to parts of it in some time, so it's always useful to make sure you're updated.

This course features more than 300 of the most commonly asked core Java interview questions that you're likely to face as an experienced software engineer. You'll get to explore questions by topic, as well as see detailed answers for each one, and plenty of live code examples where relevant. Get started today.

The Java Interview Handbook: 300+ Interview Questions

<div class="card">
   # Question # 1
    <div class="qtn">
        <p>What is an abstract class?</p>
    </div>
    <div class="ans">
        <p><span class="hi-yl-b">An abstract class can't be instantiated,  but it can be subclassed.</span> An abstract class usually contains abstract and non-abstract methods that subclasses are forced to provide an implementation for. <span class="hi-yl">An abstract method is a method that is declared without an implementation.</span> Any method marked abstract will force subclasses to provide an implementation for. Non-abstract methods will also have a method body that serves as the default implementation. Subclasses may choose to override the default implementation with their own. <span class="hi-yl-b">If a class includes abstract methods, then the class itself must be declared abstract.</span></p>
<p>Abstract classes may also implement an interface but will not be required to provide an implementation for interface methods since it can't be instantiated. Below is an example <code class="clazz">Person</code> class.</p>
## Abstract Class Example
<b>

```java
public abstract class Person implements Comparable<Person> {

    int age;
    String firstName;
    String lastName;
    String middleName;

    public Person() {

    }

    public Person(int age, String firstName, String middleName, String lastName) {
        this.age = age;
        this.firstName = firstName;
        this.middleName = middleName;
        this.lastName = lastName;
    }

    // Abstract method must be implemented by the subclass.
    abstract void printFullName();

    // Default implementation for defaultAge
    void printAge() {
        System.out.println();
    }
}
```
</b>
   </div>
</div>

<div>
   # Question # 1
    <div>
        <p>What is an abstract class?</p>
    </div>
    <div>
        <p><span>An abstract class can't be instantiated,  but it can be subclassed.</span> An abstract class usually contains abstract and non-abstract methods that subclasses are forced to provide an implementation for. <span>An abstract method is a method that is declared without an implementation.</span> Any method marked abstract will force subclasses to provide an implementation for. Non-abstract methods will also have a method body that serves as the default implementation. Subclasses may choose to override the default implementation with their own. <span>If a class includes abstract methods, then the class itself must be declared abstract.</span></p>
<p>Abstract classes may also implement an interface but will not be required to provide an implementation for interface methods since it can't be instantiated. Below is an example <code>Person</code> class.</p>
## Abstract Class Example
<b>

```java
public abstract class Person implements Comparable<Person> {

    int age;
    String firstName;
    String lastName;
    String middleName;

    public Person() {

    }

    public Person(int age, String firstName, String middleName, String lastName) {
        this.age = age;
        this.firstName = firstName;
        this.middleName = middleName;
        this.lastName = lastName;
    }

    // Abstract method must be implemented by the subclass.
    abstract void printFullName();

    // Default implementation for defaultAge
    void printAge() {
        System.out.println();
    }
}
```
</b>
   </div>
</div>

This lesson introduces the concept of abstract class in Java.

Java Ecosystem

Methods

Classes

Interfaces

Inheritance

Lambda Expressions

Generics

Multi-Threading

Memory Management

Collections

Exceptions

Reflection

Serialization

Miscellaneous Topics

Java in Practice

Patterns

The End

Abstract Classes

Question # 1