A Few Java Tricks to Myself

if ( foo.equals("bar") ) { // ... }

Here, foo may be null, so instead use

if ( "bar".equals(foo) ) { // ... }

This pattern generalizes to using the equals method of the concrete object (put the non-null object on the left side).

You can use instanceof to ensure an object is the proper type (this can replace a null check), as in

if ( arg1 instanceof String ) { // ... }

As of Java 1.5 you can declare methods with variable arity, making the syntax a little cleaner and invocation a bit simpler. The old style:

public static void main(String[] args)


public static void main(String... args)

which can then be called like this:

main("seth", "for", "president")

Errors and Exceptions derive from Throwable, so you can catch all program hiccups by catching Throwable instead of Exception (or Error).

Local variables are not initialized with a value; field variables are initialized like so:

Number primitives default to 0.

Objects (Collections) default to null.

Booleans default to false.

Java has labels, but most people will not appreciate their inclusion and use. For example, the following code is valid Java


In mixed-type computation, Java upconverts to the larger data type due to widening primitive conversion. Avoid mixed-type computation and comparisons.

“Although¬†common, the idiom object.getClass().getMethod("methodName") is broken¬†and should not be used.” – Java Puzzlers sample

The finally block of a try-catch-finally will always execute (unless there’s a hard crash, System.exit(), System.halt(), or infinite loop before). As such, be careful with returns and mutating objects in the try and finally.