In this program, you can see Java 17 multi-string (inputMessage) creating BufferedReader to read the user input (System.in). The user input inside the do-while loop will be checked and repeated until the user writes exit. For every input 1, 2, or 3 there is an specific output, but for other user inputs we get the message: “Invalid input. Valid inputs 1, 2, 3 or ‘exit’ Please try again“.
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
public class MainClassInputWhileTest {
public static void main(String[] args) throws IOException {
// Java 17 multiline string
String inputMessage = """
Please enter number from 1 - 3 or write 'exit' to stop the program.
1 get sandwich
2 get pizza
3 get water
""";
System.out.println(inputMessage);
// BufferedReader is created in try-with-resources. It will be closed automatically
try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
String line;
do {
// Read every time user input in the beginning
line = reader.readLine();
// line will be checked. If it is different from 1,2,3 or "exit" it will print
// "Invalid input. Please try again"
// Switch in Java 17 with Lambda expressions
String command = switch (line) {
case "1" -> "Here is your sandwich";
case "2" -> "Here is your pizza";
case "3" -> "Here is your water";
case "exit" -> "exit";
default -> "Invalid input. Valid input 1, 2, 3 or 'exit' Please try again";
};
System.out.println("The command is: " + command);
// do again the cycle if the user input is not "exit"
} while (!"exit".equals(line));
}
// Printing final message
System.out.println("The program exit! Goodbye!");
}
}
Console output:
Please enter number from 1 - 3 or write 'exit' to stop the program.
1 get sandwich
2 get pizza
3 get water
1
The command is: Here is your sandwich
2
The command is: Here is your pizza
3
The command is: Here is your water
4
The command is: Invalid input. Valid input 1, 2, 3 or 'exit' Please try again
a
The command is: Invalid input. Valid input 1, 2, 3 or 'exit' Please try again
exit
The command is: exit
The program exit! Goodbye!