Practical Coding in Java

//
// Basics.java
//


// This program demonstrates how to declare variables, change
// variables, and print things.


public class Basics
{
    public static void main(String[] args)
    {
        System.out.println("Hello, world!");

        // this is a comment, which is ignored by the compiler

        /*
        this is a multi-line comment, 
        which is also ignored by the compiler
        */

        // declare an integer (int) variable n

        int n = 5;
        System.out.println(n);

        // assign a new value to n

        n = 7;
        System.out.println(n);

        // variables may be a basic type (e.g. int, float, double,
        // boolean) or a reference type (e.g. String)

        float x = 1.23f;                // floating point
        System.out.println(x);

        double y = 1.23;                // double precision float
        System.out.println(y);

        boolean isHappy = true;         // boolean: true or false
        System.out.println(isHappy);

        // there are many conventions for naming variables;
        // the most important thing is to be consistent

        double my_number = 5.67;        // snake case
        System.out.println(my_number);

        double myNumber = 5.67;         // camel case
        System.out.println(myNumber);

        // helloWorld is a reference to a String object, and you
        // can use this reference to call String functions

        String helloWorld = "Hello, world!";
        System.out.println(helloWorld);
        System.out.println(helloWorld.substring(0, 4));
    }
}