Why does a null value appear in string output?

Question

When I execute the following code the output is \"nullHelloWorld\". How does Java treat null?

import java.util.*;
import java.lang.*;
import java.io.*;

/* N         


        

Answer 1

Java treats null as nothing, it is the default value of a String. It appears in your String output because you use += to add "Hello World" to str.

String str=null;
str+="Hello World";
System.out.println(str);

You are basically telling Java: give my str variable the type of String and assign it the value null; now add and assign (+=) the String "Hello World" to the variable str; now print out str