Println null argument in java

Question

One interviewer asked me this below question what is the output of the program.

But I try it in my end the line one compile but line two not compile what is the reason behind it.

Anyone can tell me please.

package swain.javainterviewhub.blogspot.in;

import java.util.Scanner;

public class JavaInterviewHub {

    public static void main(String[] args) {

        String str=null;
        System.out.println(str);//Line 1 Compile 
        System.out.println(null);/Line 2 Not compile
    }

}

What is null in real.Its string or charecter or integer.My question is what is null type. Thanks Sitansu

What error does the compiler give you? That will give you a hint as to the reason. — Cameron Skinner, Aug 24 '15 at 04:58
The method println(char[]) is ambiguous for the type PrintStream — Sitansu, Aug 24 '15 at 05:00
The compiler can't distinguish in the second case if you mean `System.out.println((Object)null)` or `System.out.println((String)null)` or indeed `System.out.println((char[])null)`. Note that there may be some other overloads of `println` that could take a `null` reference as well. — clstrfsck, Aug 24 '15 at 05:06
[3.10.7. The Null Literal](https://docs.oracle.com/javase/specs/jls/se8/html/jls-3.html#jls-3.10.7) — Jin Kwon, Aug 24 '15 at 05:48

score 7 · Accepted Answer · answered Aug 24 '15 at 04:59

7

Line two doesn't compile because System.out is a PrintStream instance, and PrintStream has more than one println method that take a reference type argument (println(String x) and println(char x[])). When you pass a null, the compiler can't decide which of the overloaded methods to choose.

System.out.println(str) passes compilation since the type of the argument (String) matches only one of the overloaded versions of println - println(String x).

answered Aug 24 '15 at 04:59

Eran

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It should be noted that you can fix this adding an explicit cast: `println((String)null)`. – Tagir Valeev Aug 24 '15 at 05:06

score 2 · Answer 2 · answered Aug 24 '15 at 05:17

2

you can cast it to make it work

System.out.println((String)null);

answered Aug 24 '15 at 05:17

Dima

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score -1 · Answer 3 · answered Aug 24 '15 at 05:00

-1

i Don't Why you are printing Null . you can Null As s String on Print Statement . You Can Use Like That :

String str=null;
System.out.println(str);//Line 1 Compile 
System.out.println("null");Print Null

answered Aug 24 '15 at 05:00

Anand Dwivedi

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Println null argument in java

3 Answers3