Java Console Examples

Use the System.out println and print methods. Read console input with System.in.

Console. An image appears on the rock wall. It glows in the darkness. It has strange text. This console window is not like most console windows.

In programs we use System.out, a stream. We read input, and write output, with this stream. And this fills many program requirements. We use println, print and other methods.

Println. This example uses the println and print methods. The println method adds a newline to the end of any output. It can even be used with no argument—this outputs only a newline.

Here: The first line is printed. The characters "A" and "B" are printed on the same line. And on the final line "C" is printed.

Java program that uses println, print public class Program { public static void main(String[] args) { System.out.println("Print line"); System.out.print("A"); System.out.print("B"); System.out.println(); System.out.println("C"); } } Output Print line AB C

Char array. The print and println methods on System.out can receive a char array. This can avoid conversions—if we have a char array, we can print it directly.

Java program that prints char array public class Program { public static void main(String[] args) { char[] array = new char[3]; array[0] = 'a'; array[1] = 'b'; array[2] = 'c'; // Print a char array. System.out.println(array); } } Output abc

Ints. For primitive types like ints, chars and doubles we do not need to convert before using print and println. There are overloads that handle these types directly.

Java program that prints ints public class Program { public static void main(String[] args) { // Print ints directly, no conversion needed. int value = 10; System.out.println(value); System.out.println(value * 10); } } Output 10 100

Append. System.out references a PrintStream. With this stream, we can append data. A CharSequence is accepted by the append method, so we can pass a string.

Subsequence: We can append a range (subsequence) with the append method. We pass the first and last indexes of the string.

Java program that uses append, System.out public class Program { public static void main(String[] args) { // Append strings to output stream. System.out.append("cat"); System.out.append("\n"); // Append range of CharSequence. System.out.append("java program", 5, 5 + 7); } } Output cat program

Read line input. We wrap a BufferedReader around System.in to read strings from the console. The syntax is complicated, but once we get an available BufferedReader, it is easy to use.

InputStreamReader: This class can be initialized from an InputStream (such as System.in).

BufferedReader: This class provides utility methods for reading from a stream. It is also used on files.

BufferedReader

Java program that reads line from console import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class Program { public static void main(String[] args) throws IOException { // Get BufferedReader for System.in. BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); // Read line from console. String line = in.readLine(); System.out.println("You typed " + line); } } Output something You typed something

Interactive program. This program uses a while-true loop to infinitely ask the user for input. It then parses the input into an int, using 0 for invalid values.While ParseInt

Switch: The program uses a switch statement to handle the user-input. The "break" statements apply to the switch statement, not the loop.

Switch

Results: When I type "cat" the default case is reached. With the lines "1" and "2" the cases labeled 1 and 2 are entered.

Java program that reads input interactively import java.io.BufferedReader; import java.io.IOException; import java.io.InputStreamReader; public class Program { public static void main(String[] args) throws IOException { // Read input with BufferedReader. BufferedReader in = new BufferedReader( new InputStreamReader(System.in)); while (true) { // Read line and try to call parseInt on it. String line = in.readLine(); int result; try { result = Integer.parseInt(line); } catch (NumberFormatException exception) { result = 0; } // Handle user input in a switch case. switch (result) { default: System.out.println("Default"); break; case 1: System.out.println("One"); break; case 2: System.out.println("Two"); break; } } } } Output cat Default 2 Two 1 One Default

Console support. Java provides robust console support. It recognizes the utility of these programs. Console programs are often harder to use, but easier to develop.

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Java Console Examples

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