TIOBE - Java Coding Standard

Rule: Design40

Synopsis:	Static java.text.Format objects should be accessed in a synchronized manner
Language:	Java
Severity Level:	2
Category:	Design

Description:

Instances of java.text.Format are generally not synchronized. Sun recommends using separate format instances for each thread. If multiple threads must access a static formatter, the formatter must be synchronized either on method or block level.

public class Foo {
    private static final SimpleDateFormat sdf = new SimpleDateFormat();
    void bar() {
        sdf.format(); // poor, no thread-safety
    }
    synchronized void foo() {
        sdf.format(); // preferred
    }
}