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The Java Interview Handbook: 300+ Interview Questions

<div class="card-quiz">
   # Question # 1
    <div class="qtn">
        <p>Consider the <code class="clazz">Printer</code> class below which is parametrized on type <code class="clazz">T</code>.</p>
<b>

```java
public class Printer<T> {

    T item;

    public Printer(T item) {
        this.item = item;
    }

    public void consolePrinter() {
        System.out.println(item.toString());
    }

    public void changeItem(T item) {
        this.item = item;
    }
}
```
</b>
</div>
</div>

Will the code compile without warnings?
<b>
  
```java
Printer printer = new Printer(5);
```
</b>

<p>Will the code compile without warnings?
<b></p>
<pre><code class="language-java">Printer printer = new Printer(5);
</code></pre>
</b>

Does the following snippet compile?
<b>
  
```java
        Printer<Integer> integerPrinter = new Printer<>(5);
        Printer rawPrinter = new Printer(new Object());
        integerPrinter = rawPrinter;
        integerPrinter.consolePrinter();
```
</b>

<p>Does the following snippet compile?
<b></p>
<pre><code class="language-java">        Printer&lt;Integer&gt; integerPrinter = new Printer&lt;&gt;(5);
        Printer rawPrinter = new Printer(new Object());
        integerPrinter = rawPrinter;
        integerPrinter.consolePrinter();
</code></pre>
</b>

prints "string item" and shows a compile time warning

What will be the output of the below snippet?
<b>
  
```java
        Printer<Integer> integerPrinter = new Printer<>(5);
        Printer printer = new Printer("my string");
        printer = integerPrinter;

        printer.changeItem("string item");
        printer.consolePrinter();
```
</b>

<p>What will be the output of the below snippet?
<b></p>
<pre><code class="language-java">        Printer&lt;Integer&gt; integerPrinter = new Printer&lt;&gt;(5);
        Printer printer = new Printer(&quot;my string&quot;);
        printer = integerPrinter;

        printer.changeItem(&quot;string item&quot;);
        printer.consolePrinter();
</code></pre>
</b>

Will the following code snippet compile, if we don't supply any type arguments?
<b>
  
```java
Printer printer = new Printer(5);
```
</b>

<p>Will the following code snippet compile, if we don’t supply any type arguments?
<b></p>
<pre><code class="language-java">Printer printer = new Printer(5);
</code></pre>
</b>

<div class="ans">
<p>The snippet <code class="mthd">Printer printer = new Printer(5);</code> will compile just fine. <span class="hi-yl-b">When the actual type parameter is omitted, a <i>raw type</i> is created</span>. Raw types show up in legacy code because lots of API classes, e.g. the Collections classes, were not generic prior to JDK 5.0. Raw types give pre-generics behavior. However, the same snippet will generate a warning for using <span class="hi-yl"><i>unchecked or unsafe operations.</i></span></p>

<p>Similarly, we can assign a raw type to a parameterized type as we do here <code class="mthd">integerPrinter = rawPrinter;</code> but the compiler will generate a warning about an unchecked operation.</p>

<p>The last snippet in the quiz above will compile and print <code class="mthd">string item</code> but a compiler warning will be generated for unchecked operations when the method <code class="mthd">changeItem()</code> is invoked on the raw <code class="clazz">Printer</code> type.

<p>The below code, when run, generates an unchecked warning. In later lessons, we'll learn how we can suppress unchecked warnings.</p> 
</div>

<div>
   # Question # 1
    <div>
        <p>Consider the <code>Printer</code> class below which is parametrized on type <code>T</code>.</p>
<b>

```java
public class Printer<T> {

    T item;

    public Printer(T item) {
        this.item = item;
    }

    public void consolePrinter() {
        System.out.println(item.toString());
    }

    public void changeItem(T item) {
        this.item = item;
    }
}
```
</b>
</div>
</div>

<div>
<p>The snippet <code>Printer printer = new Printer(5);</code> will compile just fine. <span>When the actual type parameter is omitted, a <i>raw type</i> is created</span>. Raw types show up in legacy code because lots of API classes, e.g. the Collections classes, were not generic prior to JDK 5.0. Raw types give pre-generics behavior. However, the same snippet will generate a warning for using <span><i>unchecked or unsafe operations.</i></span></p>

<p>Similarly, we can assign a raw type to a parameterized type as we do here <code>integerPrinter = rawPrinter;</code> but the compiler will generate a warning about an unchecked operation.</p>

<p>The last snippet in the quiz above will compile and print <code>string item</code> but a compiler warning will be generated for unchecked operations when the method <code>changeItem()</code> is invoked on the raw <code>Printer</code> type.

<p>The below code, when run, generates an unchecked warning. In later lessons, we'll learn how we can suppress unchecked warnings.</p> 
</div>

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

Raw Types

Question # 1