getting user input and checking if it's valid

src/main/java/fr/packageviewer/Main.java

@@ -4,6 +4,7 @@ import java.util.ArrayList;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Scanner;
 
 import fr.packageviewer.pack.SearchedPackage;
 
@@ -69,6 +70,7 @@ public class Main {
 			}
 		}
 
+		// list all packages in reverse order
 		for (int i = packets.size(); i-- > 0; ) {
 			SearchedPackage searchedPacket = packets.get(i);
 			System.out.printf("%s - %s/%s/%s %s%n\t%s%n",
@@ -79,5 +81,51 @@ public class Main {
 							  searchedPacket.getVersion()==null?"":searchedPacket.getVersion(),
 							  searchedPacket.getDescription());
 		}
+
+		System.out.printf("Pick a package to see in details (0-%s) : %n", packets.size()-1);
+		Scanner input = new Scanner(System.in);
+
+		// we create vars for the loop
+		String packetNumberString;
+		int packetNumber;
+		boolean notValid;
+		// we ask input and check if the user input is correct
+		do {
+			packetNumberString = input.nextLine();
+			// reset notValid to false, we set it in true only if something is wrong
+			notValid = false;
+			if(isNumeric(packetNumberString)) {
+				packetNumber = Integer.parseInt(packetNumberString);
+				if(packetNumber < 0 || packetNumber >= packets.size()) {
+					// this number is too big or too small
+					System.out.println("Enter a valid number");
+					notValid = true;
+				}
+			} else {
+				// this is not a number
+				System.out.println("Enter a valid number");
+				notValid = true;
+			}
+		} while(notValid);
+
+		input.close();
+
+
+	}
+
+
+	/**
+	 * Check if the String given is a number
+	 * @param i the String given
+	 * @return true if the String is a number
+	 * @author Capelier-Marla
+	 */
+	 private static boolean isNumeric(String i) {
+		try {
+			Integer.parseInt(i);
+			return true;
+		} catch (Exception e) {
+			return false;
+		}
 	}
 }