Learning Android, 2nd Edition

Chapter 2. Java Review

The purpose of this chapter is to do a quick review of Java syntax and concepts. This is not in any way a true in-depth introduction to Java (for that we suggest Oracle’s Java Tutorial). Rather, the intention is to provide a quick run-through from the very basics to more complex concepts that you will definitely need to be comfortable with in order to program for the Android platform. It is assumed that you have installed the Java Development Kit (JDK) 1.6 on the development machine (see Chapter 4 to install the JDK).

As with all opening examples for most languages, let us first cover the basic Java program and its execution with the classic “Hello World” example:

1. Open up a text editor and add the code as shown in Example 2-1.
2. Save this file as HelloWorld.java.
3. As shown in Example 2-2, compile using the javac command at a command prompt. This should create a file called HelloWorld.class.
4. Then using the java command (Example 2-2), execute the program.
5. The output should look like Example 2-3.

Example 2-1. Hello World

public class HelloWorld {

        public static void main(String[] args) {

                System.out.println("Hello World");

        }
}

Example 2-2. Hello World compile and execute

javac HelloWorld.java

java HelloWorld

Example 2-3. Hello World output

Hello World

At this stage we are looking at a really basic program that does not get into any of Java’s syntax and utility. It does contain within it the three main elements of Java: a class, a variable, and a method. A variable can ...