Software Testing: Java

When we consider a Java program it can be defined as a collection of objects that communicate via invoking each other's methods. Let us now briefly look into what do class, object, methods and instance variables mean.

Object - Objects have states and behaviors. Example: A dog has states - color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.
Class - A class can be defined as a template/ blue print that describes the behaviors/states that object of its type support.
Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed.
Instance Variables - Each object has its unique set of instance variables. An object's state is created by the values assigned to these instance variables.

First Java Program:

            public class MyFirstJavaProgram

            {  
             /* This is my first java program.  
             * This will print 'Hello World' as the output
             */
                public static void main(String []args)

                {
                   System.out.println("Hello World"); // prints Hello World
                }
            }

Let's look at how to save the file, compile and run the program. Please follow the steps given below:

Open notepad and add the code as above.
Save the file as: MyFirstJavaProgram.java.
Open a command prompt window and go o the directory where you saved the class. Assume it's C:\.
Type ' javac MyFirstJavaProgram.java ' and press enter to compile your code. If there are no errors in your code, the command prompt will take you to the next line (Assumption : The path variable is set).
Now, type ' java MyFirstJavaProgram ' to run your program.
You will be able to see ' Hello World ' printed on the window.

Hello World Program:

HelloWorld.java
public class HelloWorld
{
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}

CallingMethods :

A sample of how to call methods in the same class.

CallingMethodsInSameClass.java

Illustrates how to call static methods a class from a method in the same class

public class CallingMethodsInSameClass
{
    public static void main(String[] args) {
        printOne();
        printOne();
        printTwo();
    }

        public static void printOne() {
        System.out.println("Hello World");
    }

public static void printTwo() {
        printOne();
        printOne();
    }
}

For Loop :

A simple example of using for loops to calculate factorial. Uses the built in int data type so only good to 13!

public class Factorial
{
    public static void main(String[] args)
    {   final int NUM_FACTS = 100;
       for(int i = 0; i < NUM_FACTS; i++)
           System.out.println( i + "! is " + factorial(i));
    }

    public static int factorial(int n)
    {   int result = 1;
       for(int i = 2; i <= n; i++)
           result *= i;
       return result;
    }
}

Value Parameters :

An example that shows the behavior of value parameters. In Java all parameters are passed by value.

public class PrimitiveParameters
{
    public static void main(String[] args)
    {    go();
    }

    public static void go()
    {    int x = 3;
        int y = 2;
        System.out.println("In method go. x: " + x + " y: " + y);
        falseSwap(x,y);
        System.out.println("in method go. x: " + x + " y: " + y);
        moreParameters(x,y);
        System.out.println("in method go. x: " + x + " y: " + y);
    }

    public static void falseSwap(int x, int y)
    {    System.out.println("in method falseSwap. x: " + x + " y: " + y);
        int temp = x;
        x = y;
        y = temp;
        System.out.println("in method falseSwap. x: " + x + " y: " + y);
    }

    public static void moreParameters(int a, int b)
    {    System.out.println("in method moreParameters. a: " + a + " b: " + b);
        a = a * b;
        b = 12;
        System.out.println("in method moreParameters. a: " + a + " b: " + b);
        falseSwap(b,a);
        System.out.println("in method moreParameters. a: " + a + " b: " + b);
    }
}

String Manipulations :

A few brief examples of String manipulations.

public class StringExample
{

public static void main(String[] args)
{

       String s1 = "Computer Science";
        int x = 307;
        String s2 = s1 + " " + x;
        String s3 = s2.substring(10,17);
        String s4 = "is fun";
        String s5 = s2 + s4;
        System.out.println("s1: " + s1);
        System.out.println("s2: " + s2);
        System.out.println("s3: " + s3);
        System.out.println("s4: " + s4);
        System.out.println("s5: " + s5);
        //showing effect of precedence
        x = 3;
        int y = 5;
        String s6 = x + y + "total";
        String s7 = "total " + x + y;
        String s8 = " " + x + y + "total";
        System.out.println("s6: " + s6);
        System.out.println("s7: " + s7);
        System.out.println("s8: " + s8);
    }
}

Array :

A sample Array examples.

public class ArrayExamples
{

public static void main(String[] args)
{

int[] list = {1, 2, 3, 4, 1, 2, 3};
       findAndPrintPairs(list, 5);
       bubblesort(list);
       showList(list);

       list = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11};
       bubblesort(list);
       showList(list);

       list = new int[]{11, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, -1, -2};
       bubblesort(list);
       showList(list);

       list = new int[]{1};
       bubblesort(list);
       showList(list);
    }

Software Testing

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Java