With the help of I/O routines the programmer can interact with the program. Among other things, he can query the program status or control the program flow with inputs. The simplest screen output is handled in Java as follows: System.out.print()
or System.out.println()
Variables can be appended to the output string using the +
operator.
public class OutputStream {
public static void main(String[] args) {
System.out.print("Output ");
System.out.println("stream");
System.out.println("new line");
System.out.printf("new line\n");
System.out.println(4 + 5);
System.out.println("Number: " + 6);
}
}
Output stream
new line
new line
9
Number: 6
Line | Description |
---|---|
3 | Declares and initializes the variables a and b of type int with the values 2 and 4 |
5 | The println() method outputs a string. The + operator can be used to represent variable values. |
public class OutputStream {
public static void main(String[] args) {
int a = 2, b = 4;
System.out.println("First number " + a + ", second number: " + b);
}
}
First number 2, second number: 4
With the help of the java Scanner
class screen inputs can be read in Java. By creating an object of the Scanner
class, you have the possibility to take the input value of certain data types over this object. If an object of the Scanner
class is no longer needed, it should be closed with the close()
method. Otherwise, a memory space is reserved until the end of the program.
Scanner input = new Scanner(System.in);
int val = input.nextInt();
String str = input.next();
char c = input.next().charAt(2);
double d = input.nextDouble();
float f = input.nextFloat();
boolean b = input.nextBoolean();
...
Line | Description |
---|---|
5 | Creates an object of type Scanner named input with predefined standard input object (System.in ) |
6 | The methods of the Scanner class can be accessed through the previously created Scanner object. nextInt() waits for user input. Then we store the input in the variable val |
8 | Outputs the entered number |
import java.util.Scanner;
public class InputStream {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int val = input.nextInt();
System.out.println("Entered value: " + val);
}
}
5
Entered value: 5
Line | Description |
---|---|
5 | Creates an object of type Scanner named input with predefined standard input object (System.in ) |
6 | Creates the variables a , b and result of type integer |
8 – 9 | Prompts the user to enter a number. The methods of the Scanner class can be accessed via the previously created Scanner object (input ). nextInt() waits for a user input. Then we store the input in variable a |
11 – 12 | Prompts the user to enter a second number, which is then stored in variable b |
14 | Closes the Scanner object input and terminates user input |
16 | Stores the sum of variable a and b in the variable result |
18 | Outputs the result including the calculation |
import java.util.Scanner;
public class InputOutput {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int a, b, result;
System.out.print("Please enter first number: ");
a = input.nextInt();
System.out.print("Please enter second number: ");
b = input.nextInt();
input.close();
result = a + b;
System.out.println(a + " + " + b + " = " + result);
}
}
Please enter first number: 5
Please enter second number: 8
5 + 8 = 13