What happens When System.out.println(null)?

• Compilation Error -This is because you can pass an Object or a String or char[]. Since null can fit in both, the compiler doesn't know which method to use, leading to compile error.


• Method Overloading:
      1.public void prinltln(String str) { }
      2.public void prinltln(char[] ch){ }
      3.public void prinltln(Object ch){ 
•  It seems the call System.out.print(null) is ambiguous to compiler because print(null) here will find the two best specific matches i.e. print(String) and print(char[]) . So compiler is unable to determine which method to call here .
• Compilation Error:
     System.out.println(null)

Program #1: what will happen when we print System.out.println(null)

• Compile Fine:
       System.out.println((String)null);//null
       System.out.println((char[])null);
       System.out.println((Object)null);//null
• It's the compiler type-checking the parameters of the method call.
• But here we need to know one more thing  System.out.println((char[])null); will compile fine but at run time will throw runtime exception.

 Program #2: what will happen when we print System.out.println(null) by type casting
  

1. package com.systemoutprintn;
2. public class Test {
3.  
4.     /**
5.      * @Website: www.instanceofjava.com
6.      * @category: System.out.println(null)
7.      */
8.  
9. public static void main(String[] args) {
10.  
11.          System.out.println((String)null);//null
12.          System.out.println((Object)null);//null
13.          System.out.println((char[])null);
14.             
15.  
16. }
17.  
18. }

 Output:
 

1. null
2. null
3. Exception in thread "main" java.lang.NullPointerException
4.     at java.io.Writer.write(Unknown Source)
5.     at java.io.PrintStream.write(Unknown Source)
6.     at java.io.PrintStream.print(Unknown Source)
7.     at java.io.PrintStream.println(Unknown Source)
8.     at com.systemoutprintn.Test.main(Test.java:13)