Java I/O

Print Streams

System.out and System.err are instances of the java.io.PrintStream class. This is a subclass of FilterOutputStream that converts numbers and objects to text. System.out is primarily used for simple, character-mode applications and for debugging. Its raison d'être is convenience, not robustness; print streams ignore many issues involved in internationalization and error checking. This makes System.out easy to use in quick and dirty hacks and simple examples, while simultaneously making it unsuitable for production code, which should use the java.io.PrintWriter class (discussed in Chapter 15) instead.

The PrintStream class has print() and println() methods that handle every Java data type. The print() and println() methods differ only in that println() prints a platform-specific line terminator after printing its arguments and print() does not. These methods are:

public void print(boolean b)
public void print(char c)
public void print(int i)
public void print(long l)
public void print(float f)
public void print(double d)
public void print(char[] s)
public void print(String s)
public void print(Object o)
public void println()
public void println(boolean b)
public void println(char c)
public void println(int i)
public void println(long l)
public void println(float f)
public void println(double d)
public void println(char[] s)
public void println(String s)
public void println(Object o)

Anything at all can be passed to a print() method; whatever argument you give is guaranteed ...