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 type inference?</p>
    </div>
    <div class="ans">
        <p><span class="hi-yl-b">Type inference is Java compiler's ability to look at each method invocation and corresponding method declaration to determine the type argument, or arguments that make the invocation applicable.</span> The inference algorithm determines the types of the arguments and, if available, the type of the result being assigned, or returned. Consider the useless but instructional class below:</p>
<b>

```java
public class InferenceExample {

    public <U> U identity(U item) {
        return item;
    }
}
```
</b>
<p>Without the compiler's inference superpower, you'll need to write verbose code like below to use the <code class="mthd">identity()</code> method:</p>
<b>

```java
        InferenceExample inferenceExample = new InferenceExample();
        double g = inferenceExample.<Double>identity(45d);
```
</b>
<p><span class="hi-yl-b">Note that the angle brackets with the type <code class="clazz">&lt;Double&gt;</code> is called the <b><i>type witness</i></b>.</span> Type inference allows us to skip writing out the type witness since the compiler can infer from the context that the type parameter <code class="clazz">U</code> is a <code class="clazz">Double</code>.</p>
<b>

```java
        InferenceExample inferenceExample = new InferenceExample();
        double f = inferenceExample.identity(55d);
```
</b>
</div>
</div>


<div>
   # Question # 1
    <div>
        <p>What is type inference?</p>
    </div>
    <div>
        <p><span>Type inference is Java compiler's ability to look at each method invocation and corresponding method declaration to determine the type argument, or arguments that make the invocation applicable.</span> The inference algorithm determines the types of the arguments and, if available, the type of the result being assigned, or returned. Consider the useless but instructional class below:</p>
<b>

```java
public class InferenceExample {

    public <U> U identity(U item) {
        return item;
    }
}
```
</b>
<p>Without the compiler's inference superpower, you'll need to write verbose code like below to use the <code>identity()</code> method:</p>
<b>

```java
        InferenceExample inferenceExample = new InferenceExample();
        double g = inferenceExample.<Double>identity(45d);
```
</b>
<p><span>Note that the angle brackets with the type <code>&lt;Double&gt;</code> is called the <b><i>type witness</i></b>.</span> Type inference allows us to skip writing out the type witness since the compiler can infer from the context that the type parameter <code>U</code> is a <code>Double</code>.</p>
<b>

```java
        InferenceExample inferenceExample = new InferenceExample();
        double f = inferenceExample.identity(55d);
```
</b>
</div>
</div>


This lesson explains the concept of type inference.

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

Type Inference

Question # 1