CBSE Book Class 11 Informatics Practices Programming Fundamentals

Programming Fundamentals

Variables

After observing the above form, it is clear that we are accepting the number of apples, bananas and oranges in three separate text fields and calculating the total number of fruits by simply adding the three values on the click of a button. The total number of fruits is then displayed in a separate text field.

Now imagine a situation where we have to calculate the total of 20 such fruits. Our one line of code will become very cumbersome and difficult to understand. To avoid such cumbersome code we need to use some containers, which can store the values entered by the user in the different text fields. These values need to be stored only till we add them up. So we need to modify the code given above. To test the same we first need to design the form and then associate code with the click of the button.

Let us first talk about the design of the form. Add a new JFrame form. Go to the Properties tab in the Palette Window and change the title property of the Form as shown in the Figure 5.3.

Now add the following components on the form: three editable text fields to accept the number of apples, bananas and oranges two buttons - one to calculate & display the total number of fruits and one to exit from the application one non-editable text field to display the total number of fruits appropriate labels to direct the user Change the properties of the components as learnt in the previous chapter so that the form looks exactly like the one displayed in Figure 5.1. The next step is to associate code with the button with display text "Number ofFruits".Double click on the button in the design window to reach the point in the source window where the code needs to be written. Rewrite the code given in Figure 5.2 using the concept of containers as shown in Figure 5.4.

How many containers did we use to solve the above problem? We used four containers. Three of them were used to store the number of individual fruits and the fourth one was used to store the total number of fruits. These four containers need to be identified using separate names. In the beginning of the program, the containers were empty but during the execution, we changed their initial values and allocated different values to them. Such containers are called variables. From the above exercise we infer that these containers/variables have four special characteristics:

1. They have a name.

2. They are capable of storing values.

3. They provide temporary storage.

4. They are capable of changing their values during program execution.

Thus, variables are named temporary storage areas capable of storing values, which can change during the execution of the program. Remember, variables are declared within the code that uses them. In the above code the values are entered by the user in the three textFields and then these values are assigned (stored) to the variables Apples, Bananas and Oranges after converting the values to type Integer using the ParseInt() method. The statement used to assign the values is:

Apples=Integer.ParseInt(jTextField1.getText());

In this case the value entered in jTextField1 is assigned to variable Apples. Similarly, values entered in jTextField2 is stored in the variables called Bananas and value entered in jTextField3 is stored in the variables called Oranges. The sum total is stored in the variable Fruits using the statement:

Fruits = Apples + Bananas + Oranges;

Again observe the code given in Figure 5.4 closely and try to find out one extra characteristic about the variables. Note that they all have been used to store numbers without decimals. What if we change the application above to find the total marks obtained by a student? In that case the variables will store numbers with decimals. Whatif we change the above application to accept the first name, middle name and last name of the user and want to display the full name in the fourth text field? In that case the variables will have to store groups of characters. What do we learn from this? We learn a new characteristic of these variables - each variable can store a specific type of data. The type of data that a variable is capable of storing guides us about how to handle that particular variable and also informs us about what can be done with these variables. So each variable has a specific data type, which determines the kind of value they can store, and also specifies what can be done with these variables. Each programming language has a set of data types that can be used according to the need of the programmer. Now that we are clear about the facts why we need variables and the use of data types, let us try and understand the different data types available in java. In the above example all four variables- Apples, Bananas, Oranges and Fruits are integer type variables as they are storing numbers without decimals. In the code given in Figure 5.4 can you point out the keyword, which identifies these variables as integer numbers?

Data Types

The keyword used to identify the variables as integers is int. These are variables without decimals. Similarly we have data types for handling other varieties of data. The different types of data that we enter need different type of handling. These different types of data can be manipulated through specific data types.

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