Question

Write an application that inputs a line of text, tokenizes the line with String method split and outputs the tokens in reverse order. Use space characters as delimiters.

Short answer

Get input, use split(' '), reverse the token array, output the tokens.

Step-by-step solution

Import Required Libraries

Begin by importing the necessary libraries for the program to run. Since we are making a simple application that doesn't require external libraries, we don't need to import anything for this exercise.

Get User Input

Prompt the user to enter a line of text. Use a scanner, BufferedReader or any other input class in your programming language to read the input from the user.

Tokenize the Line

Use the String method split with a space character (' ') as the delimiter to divide the input line into tokens. This will return an array of tokens.

Reverse the Tokens

Reverse the order of tokens. You could create a new array for this purpose or reverse the existing array in place.

Output the Tokens in Reverse Order

Iterate through the array of tokens in reverse order, and output each token. If you've chosen to reverse the array itself, simply iterate in the normal forward direction.

Key concepts

String method split

In Java, processing text often involves dealing with individual elements, such as words or sentences, within a larger string. The split() method of the String class is a powerful tool for this. It breaks up a string into multiple parts, called tokens, based on a specified delimiter. For instance, given a phrase like 'learning Java is fun', and using a space (' ') as the delimiter, the split() method would tokenize this into an array of strings containing ['learning', 'Java', 'is', 'fun'].

Using this method is straightforward and can be highly useful in various applications, such as text analysis, natural language processing, or simply formatting input. It's important to remember that the delimiter can be anything from a single character to a regular expression, which offers flexibility for complex string tokenization tasks.

Input handling in Java

Proper input handling is crucial in any Java application that requires user interaction, such as the one described in the exercise. There are several ways to handle input in Java; among the most common ones are using the Scanner class or BufferedReader with InputStreamReader.

Handling User Input with Scanner

The Scanner class is widely used for reading input values from various sources like input streams, files, or strings. For example, a new Scanner object could be created, linked to System.in, to read user input from the console. It provides various methods to read different data types but for a line of text, nextLine() would be used.

Using BufferedReader for User Input

Alternatively, the BufferedReader class combined with an InputStreamReader and System.in provides a buffered approach to input handling. This can be beneficial when dealing with large amounts of data because it reduces the number of interactions with the underlying reader.

Array manipulation in Java

Arrays are a fundamental data structure in Java, and handling them effectively is key to many programming tasks. In the context of the given exercise, after tokenizing a string using the split() method, we get an array of strings. To reverse this array, we may either create a new array and fill it with elements from the original one in reverse order, or reverse the original one in place.

Reversing an array in place typically involves swapping elements from both ends of the array, moving towards the center. It's an efficient way to handle the reversal as it doesn't require extra memory. However, when the original order needs to be preserved, or the reversal operation might be done multiple times, creating a new array might be a better approach.

Iterating through arrays in Java is also straightforward. For example, to print out the tokens in reverse order, one could use a simple for-loop that starts from the end of the array and decrements the index until it reaches the first element. This is a common strategy for array manipulation that is both efficient and easy to understand.