Help with try and catch

Question

I know I posted this quesiton earlier,but I am sitll having problems. In the following code, the exception IS caught if the user enters a String instead of a Int. But the Exception is NOT caught if the user enters
the "Enter" key.
            do
                          flag=false;
                 //set the quantity to user input                                                   
                 System.out.print("Enter the quantity:");
                 try
                   amount = input.nextInt();
                      if (amount > 0)  //executes when amount is less then or equal to zero
                         flag=false; 
                      } //end of if
                      else
                           System.out.println("You must enter a positive quantity");
                                          flag=true;
                 }  //end of try
                 catch (Exception e)
                                  input.nextLine();
                                  System.out.println("You must enter a number");
                                  flag=true;
            }while(flag==true);  //end of do while
                      

Answer 1

nextInt won't read "just the enter key"... it blocks until reads "something".
Try something like this instead...
Note: java.io.Console is new in 1.6
package krc.utilz.io;
// usage:
// import krc.utilz.io.Console;
// String name = Console.readLine("Enter your name : ");
// while ( (score=Console.readInteger("Enter a score between 0 and 100 (enter to quit) : ", 0, 100, -1)) != 1) { ... }
import java.util.Date;
import java.text.DateFormat;
import java.text.SimpleDateFormat;
public abstract class Console
  private static final java.io.Console theConsole = System.console();
  private static final DateFormat dateFormatter = new SimpleDateFormat("dd/MM/yyyy");
  public static String readLine(String prompt) {
    while(true) {
      try {
        System.out.print(prompt);
        return theConsole.readLine();
      } catch (Exception e) {
        System.out.println("Oops: "+e);
  public static Date readDate(String prompt) {
    while(true) {
      try {
        String response = readWord(prompt+" (dd/mm/yyyy) : ");
        return dateFormatter.parse(response);
      } catch (Exception e) {
        System.out.println("Oops: "+e);
  public static String readWord(String prompt) {
    String response = null;
    while(true) {
      try {
        response = readLine(prompt);
        if( response!=null && response.length()>0 && response.indexOf(' ')<0 ) break;
        System.out.println("A single word is required. No spaces.");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
    return(response);
  public static char readLetter(String prompt) {
    char c = '\0';
    while(true) {
      try {
        String response = readLine(prompt);
        if ( response!=null && response.length()>0 ) {
          c = response.charAt(0);
          if(Character.     isLetter(c)) break;
        System.out.println("A letter (A through Z) is required. Upper or lower case.");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
    return(c);
  public static int readInteger(String prompt) {
    int i = 0;
    String response = null;
    while(true) {
      try {
        response = readLine(prompt);
        if ( response!=null && response.length()>0 ) {
          i = Integer.parseInt(response);
          break;
        System.out.println("An integer is required.");
      } catch (NumberFormatException e) {
        System.out.println("\""+response+"\" cannot be interpreted as an integer!");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
    return(i);
  public static int readInteger(String prompt, int lowerBound, int upperBound) {
    int i = 0;
    while(true) {
      i = readInteger(prompt);
      if ( i>=lowerBound && i<=upperBound ) break;
      System.out.println("An integer between "+lowerBound+" and "+upperBound+" (inclusive) is required.");
    return(i);
  public static int readInteger(String prompt, int defualt) {
    int i = 0;
    String response = null;
    while(true) {
      try {
        response = readLine(prompt);
        return (response!=null && response.trim().length()>0
          ? Integer.parseInt(response)
          : defualt
      } catch (NumberFormatException e) {
        System.out.println("\""+response+"\" cannot be interpreted as an integer!");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
  public static int readInteger(String prompt, int lowerBound, int upperBound, int defualt) {
    int i = 0;
    while(true) {
      i = readInteger(prompt, defualt);
      if ( i==defualt || i>=lowerBound && i<=upperBound ) break;
      System.out.println("An integer between "+lowerBound+" and "+upperBound+" (inclusive) is required.");
    return(i);
  public static double readDouble(String prompt) {
    double d = 0;
    String response = null;
    while(true) {
      try {
        response = readLine(prompt);
        if ( response!=null && response.length()>0 ) {
          d = Double.parseDouble(response);
          break;
        System.out.println("A number is required.");
      } catch (NumberFormatException e) {
        System.out.println("\""+response+"\" cannot be interpreted as a number!");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
    return(d);
  public static double readDouble(String prompt, double lowerBound, double upperBound) {
    while(true) {
      double d = readDouble(prompt);
      if ( d>=lowerBound && d<=upperBound ) return(d);
      System.out.println("A number between "+lowerBound+" and "+upperBound+" (inclusive) is required.");
  public static boolean readBoolean(String prompt) {
    while(true) {
      try {
        String response = readWord(prompt+" (Y/N) : ");
        return response.trim().equalsIgnoreCase("Y");
      } catch (Exception e) {
        System.out.println("Oops: "+e);
}