Merge pull request utkarsh-shekhar#56 from techpavan/master

utkarsh-shekhar · web-flow · commit 9fea604e2037 · 2017-10-17T10:44:25.000+05:30
Java code to check if a given number is prime.
diff --git a/java/PrimeCheck.java b/java/PrimeCheck.java
@@ -0,0 +1,43 @@
+import java.util.InputMismatchException;
+import java.util.Scanner;
+
+/**
+ * To check whether a given number is prime
+ */
+public class PrimeCheck {
+
+    public static void main(String[] args) {
+
+        // Accept input from the console
+        System.out.print("Please enter a natural number: ");
+        int num = 0;
+        try {
+            Scanner sc = new Scanner(System.in);
+            num = sc.nextInt();
+            sc.close();
+        } catch (InputMismatchException e) {
+            outputAndEnd("Input not valid, expected a natural number."); // Error message for all non numerical inputs
+        }
+
+        if (num < 0) {
+            outputAndEnd("Input not valid, natural number expected"); // Error message for all negative inputs
+        } else if (num < 2) {
+            outputAndEnd("0 and 1 are neither prime nor composite"); // Info message for 0 and 1
+        }
+
+        // Check if the given number is divisible from any number between 2 and num/2, if so, its composite
+        for (int i = 2; i <= num / 2; i++) {
+            if (num % i == 0) {
+                outputAndEnd(num + " is not a prime number."); // Output result and exit as we found one divisor other than 1 and itself
+            }
+        }
+        // The number has exit the loop with no divisors, which means it is a prime number, print success message.
+        outputAndEnd(num + " is a prime number.");
+    }
+
+	// A method to print the given message and exit the program
+    private static void outputAndEnd(String message) {
+        System.out.println(message); // output the given message
+        System.exit(0); // exit the program
+    }
+}
