Java BufferedReader create from InputStreamReader and System.in to read console input
import java.io.BufferedReader; import java.io.InputStreamReader; public class Main { public static void main(String args[]) throws Exception { InputStreamReader isr = new InputStreamReader(System.in); BufferedReader br = new BufferedReader(isr); while (true) { System.out.print("Radius? "); String str = br.readLine(); double radius; try {/*from w ww. jav a2s. c o m*/ radius = Double.valueOf(str).doubleValue(); } catch (NumberFormatException nfe) { System.out.println("Incorrect format!"); continue; } if (radius <= 0) { System.out.println("Radius must be positive!"); continue; } System.out.println("radius " + radius); return; } } }