Added Goldbach's Conjecture algorithm.

src/main/java/com/thealgorithms/maths/GoldbachConjecture.java

@@ -0,0 +1,55 @@
+package com.thealgorithms.maths;
+
+import static java.lang.String.format;
+
+import java.util.Scanner;
+
+/**
+ * This is a representation of the unsolved problem of Goldbach's Projection, according to which every
+ * even natural number greater than 2 can be written as the sum of 2 prime numbers
+ * More info: https://en.wikipedia.org/wiki/Goldbach%27s_conjecture
+ * @author Vasilis Sarantidis (https://github.com/BILLSARAN)
+ */
+
+public final class GoldbachConjecture {
+    private GoldbachConjecture() {
+    }
+
+    /**
+     * Checks whether a number is prime or not
+     * @param n the input number
+     * @return true if n is prime, else return false
+     */
+    private static boolean isPrime(int n) {
+        int i;
+        if (n <= 1 || (n % 2 == 0 && n != 2)) {
+            return false;
+        } else {
+            for (i = 3; i < Math.sqrt(n); i += 2) {
+                if (n % i == 0) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    public static void main(String[] args) {
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.println("Enter a number");
+        int n = scanner.nextInt();
+        int flag = 0;
+
+        if (n % 2 == 0 && n > 2) {
+            for (int i = 0; i <= n / 2 && flag == 0; i++) {
+                if (isPrime(i) && isPrime(n - i)) {
+                    System.out.println(format("%d + %d = %d", i, n - i, n));
+                    flag = 1;
+                }
+            }
+        } else {
+            System.out.println("Wrong Input");
+        }
+    }
+}