Java Tips

Java language fundamentals

There should be at most one public class definition per source file, the filename must match the name of the public class.

keyword - a word whose meaning is defined by the programming language

true and false aren't in fact keywords, they are literal boolean values

goto and const are reserved words

identifier - is a word used by a programmer to name a variable, method, class or label. Must begin with a letter, a dollar sign or underscore

Java's four signed integral data types are: byte, short, int, long

Double and float can take on values that are bit patterns that do not represent numbers
Float.NaN, Float.NEGATIVE_INFINITY, Float.POSITIVE_INFINITY.. the same with Double

A literal is a value specified in the program source, they cannot appear on the left side of assignments.

A Java array is an ordered collection of primitives, object references or other arrays, all elements must be of the same type. To create and use an array you must follow three steps: Declaration, Construction, Ininialization. 1. int[] integers, 2. integers = new int[20]

Java array is starting with index 0.

A common mistake is to guess that importing has something to do with class loading. The fact is, that the name is brought into the source file's namespace.

import static java.awt.Color.RED; ... myColor = RED; ... Static imports eliminate the nuisance of constant interfaces.

import static measure.Scales.kilometersToMiles();

Member variable - is created when the instance is created, and exists as long the enclosing object exists. Automatic variable - is created on entry to the method. Class variable - (aka. static variable) is created when the class is loaded and is destroyed when the class is unloaded. Initial value is assigned to member variables, static variables, but not automatic variables.

When java passes an argument into a method call, a copy of the argument is actually passed.

Each process has its own stack and heap. Objects are always allocated on the heap.

Explicitly assign null into a variable when you have finished with it.

When the garbage collector finds memory that is no longer accessible from any live thread it takes steps to release it back into the heap for re-use. Class destructor method is called finalize().

It is not possible to force the garbage collection.

Importing slightly increases compilation time.

In Java all arguments are passed by value.