Programming in Java Netbeans - A Step by Step Tutorial for Beginners: Lesson 19

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Welcome to lesson 19 of this tutorial on Programming in Java. Having looked into arrays in Java in our previous lessons and how we can manipulate arrays in Java, in this particular lesson we shall look at how we can take advantage of the many methods that ship in with Java to manipulate data of string type. In particular, we shall look at methods to convert strings into uppercase and lowercase.

Unlike int variables, or double variables, strings variables are objects, that means you can manipulate data of string type in more different ways than you can do with other data types such as int, double, boolean, byte, single, char or float variables.

Strings in Java are represented by series of Unicode characters under a variable name and Unicode values are stored as hexadecimals numbers.

Capital letters (A to Z) are stored using hexadecimals values \u0041 to \u005a, while lowercase letters (a to z) are stored using hexadecimals values \u0061 to \u007a.

To convert strings into uppercase in Java, we use the inbuilt toUpperCase() method in Java. Let us write a simple program in Java that stores string characters in lowercase and then use the method to convert the strings into uppercase. Create a new Java class called ChangeToUpper and write the following code.

In the above program, we have defined a variable of string type called mystring using the following statement.

String mystring = "How are you";

In the first output using JoptionPane, we output the string as it is i.e "How are you". In the second output we first convert the string into uppercase and then output the same string but in uppercase.

JOptionPane.showMessageDialog(null, mystring);

mystring = mystring.toUpperCase();

JOptionPane.showMessageDialog(null, mystring);

Now, modify the program or create another Java class called ChangeToLower as shown above. Change the string variable to be in uppercase and then use the method toLowerCase() to convert the string into lowercase and output. In the next lesson, we shall learn how we can compare strings in Java.

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