Question

Write an application that inputs a line of text and outputs the text twice -once in all uppercase letters and once in all lowercase letters.

Short answer

Get input, convert to uppercase and lowercase, then print both.

Step-by-step solution

Get User Input

Prompt the user to input a line of text. This can be done using a function like `input()` in many programming languages. Store the input in a variable, for example, `user_text`.

Convert to Uppercase

Use a string method or function to convert the user input to all uppercase letters. In many languages, you can use a method like `upper()`. For instance, use `user_text.upper()` to get the uppercase version of the input. Store this in a variable, let's say `uppercase_text`.

Convert to Lowercase

Similarly, use a string method or function to convert the user input to all lowercase letters. You might use a method like `lower()`. For example, `user_text.lower()` will return the lowercase version of the input. Store this in a variable called `lowercase_text`.

Output the Results

Print or display the results. First, output the `uppercase_text`, followed by `lowercase_text`. This can be done with a print function, such as `print(uppercase_text)` and `print(lowercase_text)` to show both versions of the input text.

Key concepts

User Input

In Java programming, handling user input is essential, especially when creating interactive applications. To capture user input, you typically use the `Scanner` class. The `Scanner` class is a part of the `java.util` package, which provides methods to read user input of various data types from different input sources like the keyboard, files, or streams. To use this class, you need to create an instance of it. This is usually done by linking it to the standard input stream, `System.in`.
For example:
```java Scanner scanner = new Scanner(System.in); ```
This piece of code is telling the Java program to watch the keyboard for input. When you're ready to read a line of text from the user, you can call the `nextLine()` method on the `scanner` object.
For example:

• `String userInput = scanner.nextLine();`

This command will halt the program and wait for the user to type something and press ENTER. The text typed in by the user is then stored in the `userInput` variable.
Capturing user input is crucial for making your applications dynamic and responsive.

String Manipulation

Working with strings is one of the fundamental aspects of Java programming, often involving modifying and examining text values. String manipulation refers to the processes of altering and handling the data stored within string variables. Java provides various in-built methods to make string manipulation straightforward and efficient.
One common manipulation is changing the case of the letters in a string. The Java String class offers methods such as `toUpperCase()` and `toLowerCase()`, which are used to transform all letters in a string to their uppercase or lowercase equivalents, respectively.

• `String upperCaseText = userInput.toUpperCase();`
• `String lowerCaseText = userInput.toLowerCase();`

This demonstrates how easily we can convert text case in Java. These methods do not alter the original string but return a new string with the modifications.
It's essential to recognize that Java strings are immutable, meaning once a string object is created, it cannot be changed. Hence, methods like `toUpperCase()` and `toLowerCase()` create and return new string instances.
Proper understanding of string manipulation helps in performing complex text operations, such as formatting, encrypting, or parsing data.

Text Transformation

In programming, text transformation is the process of altering the presentation or content of text. This is particularly useful when you need to display text in different formats or ensure consistency in text processing. As demonstrated earlier, transforming text between upper and lower case is a straightforward example of text transformation.
Understanding text transformation is crucial for applications that deal with text input and output. For instance, making text uppercase could be useful for visual emphasis, or converting text to lowercase might be necessary for case-insensitive comparisons in your program.
Beyond case transformation, text manipulation in Java encompasses methods for trimming whitespace (`trim()`), checking for text equality (`equals()`), and searching for substrings (`contains()` or `indexOf()`). Each of these methods transforms or interrogates text in a way that's essential for many programming tasks.
For example, you might need to remove leading or trailing spaces for correct user input processing, which can be done using:

• `String trimmedText = userInput.trim();`

By mastering text transformation techniques in Java, one can efficiently handle and transform data, making your programs more robust and versatile.