The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Dev.java for updated tutorials taking advantage of the latest releases.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.

Writing Diagnostics to Standard Output and Error Streams

A Java applet can write messages to the standard output and standard error streams. Writing diagnostics to standard output can be an invaluable tool when you are debugging a Java applet.

The following code snippet writes messages to the standard output stream and the standard error stream.

// Where instance variables are declared:
boolean DEBUG = true;
// ...
// Later, when we want to print some status:
if (DEBUG) {
 try {
 // ...
 //some code that throws an exception
 System.out.
 println("Called someMethod(" + x + "," + y + ")");
 } catch (Exception e) {
 e.printStackTrace()
 }
}

Check the Java Console log for messages written to the standard output stream or standard error stream. To store messages in a log file, enable logging in the Java Control Panel. Messages will be written to a log file in the user's home directory (for example, on Windows, the log file might be in C:\Documents and Settings\someuser\Application Data\Sun\Java\Deployment\log).