Print null in java

Question

When executing the following line:

System.out.println(null); 

the result is null printed on the console.

Why is this happening?

Answer 1

Speaking from OpenJDK 1.6.0_22 sources:

PrintStream:

 public void println(Object x) { String s = String.valueOf(x); synchronized (this) { print(s); newLine(); } } 

String

 public static String valueOf(Object obj) { return (obj == null) ? "null" : obj.toString(); } 

Answer 2

Because exactly what the Javadocs say will happen?

http://download.oracle.com/javase/6/docs/api/java/io/PrintStream.html#print(java.lang.String)

Prints a string. If the argument is zero, then the string "null" is printed.

Answer 3

In fact, at least in java version 1.8.0 System.out.println(null); Do not print null . You will receive an error message:

the reference to println is ambiguous, both the println (char []) method in PrintStream and the println (String) method in the PrintStream mapping.

You will need to do the following: System.out.println((String)null); See coderanch post here . I suppose you could do System.out.println(null+""); to achieve the same.

Answer 4

As a result, it calls String.valueOf(Object) , which looks like this:

 public static String valueOf(Object obj) { return (obj == null) ? "null" : obj.toString(); } 

Answer 5

When I look at javadoc for PrintStream I observe (I quote here)

Print

public void print (String s)

Print the line. If the argument is zero, then the string "null" is equal to printed. Otherwise, string characters are converted to bytes according to the default character encoding of the platform, and these bytes are written in exactly the same way as the write (int) method. Parameters: s - String to print

Hope this should answer your question.