My Favorite Java Tricks and Tips

•  Classpath wild cards since Java 6: java -classpath ./lib/* so.Main Instead of java -classpath ./lib/log4j.jar:./lib/commons-codec.jar:./lib/commons-httpclient.jar:./lib/commons-collections.jar:./lib/myApp.
• JDK 1.6_07+ contains an app called VisualVM (bin/jvisualvm.exe)
• variable arity. So, instead of just passing an array, now you can do the following

  public void foo(String... bars) {
     for (String bar: bars)
        System.out.println(bar);
  }

  bars is automatically converted to array of the specified type

•  javap disassembler which comes with Sun's JDK is not widely known or used.
• // For each Object, instantiated as foo, in myCollection

for(Object foo: myCollection) {
  System.out.println(foo.toString());
}

• checking for null is not necessary.

Instead of:

if( null != aObject && aObject instanceof String )
{
    ...
}

just use:

if( aObject instanceof String )
{
    ...
}

• anonymous subclass or anonymous impl of an interface:

public void initAnonymousSubclass() {
//anonymous subclass and directly call a method on it even if it implements no interfaces.
new Thread() {
public void run() {
while (true) {
try {
Thread.sleep(2000);
System.out.println("sleeping");
} catch (InterruptedException e) {
e.printStackTrace();
}
}

}
}.start();
}

public void initImplementationOfInterface(){
new TestInterface(){

@Override
public String printId() {
// TODO Auto-generated method stub
String someString = "time "+System.currentTimeMillis();
System.out.println(someString);
return someString;
}

}.printId();
}

Source attributation: http://stackoverflow.com/questions/15496/hidden-features-of-java