Core java interview Questions You'll Most Likely Be Asked (Second Edition)

Identify the error in the following code snippet and explain
how it can be fixed.
public interface MyInterface {
public static void doSomething() {
System.out.println(“Doing something....”);
}
}
public class MyClass implements MyInterface{
public static void main(String args[]) {
MyClass obj = new MyClass();
obj.doSomething(); //Line 1
}
}
Answer:

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The code above defines an interface called MyInterface with a
static method called doSomething(). It then creates a class
called MyClass which implements MyInterface. The main
method of MyClass creates an object of MyClass called obj
and invokes the doSomething() method at Line 1. This causes
a compilation error at Line 1. This is because the code tries to
access a static interface method via an object of the class. Static
interface methods can only be accessed via the interface name.
In order to fix the error, Line 1 needs to be replaced as follows:
MyInterface.doSomething();

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247.
248.
CHAPTER
07
Optionals
What is an Optional and why was it added by Java 8?
Answer:
An Optional is used to represent a value that can either be
present or absent. It has methods that can be used to retrieve the
underlying value if present. The following code demonstrates an
Optional:
Optional number;
So here, number is an Optional of type Integer. It may or may
not contain a value.
Optionals were added by Java 8 to avoid the boilerplate code
associated with null checks. Sometimes, a method may return a
null. This can result in a NullPointerException. In order to
avoid the exception, the code that invokes the method needs to
have explicit null checks. This can make the code difficult to read.
Java 8 Optionals help to avoid this boilerplate code. So instead of
having an explicit null check, an optional can be used. If the value
is present it can be retrieved.