Added Goldbach's Conjecture algorithm.

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

@@ -0,0 +1,40 @@
+package com.thealgorithms.maths;
+
+import static com.thealgorithms.maths.PrimeCheck.isPrime;
+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() {
+    }
+
+    public static String getPrimeSum(int number) {
+        String s1;
+        if (number % 2 == 0 && number > 2) {
+            for (int i = 0; i <= number / 2; i++) {
+                if (isPrime(i) && isPrime(number - i)) {
+                    s1 = format("%d + %d = %d", i, number - i, number);
+                    return s1;
+                }
+            }
+        }
+        return "Wrong Input";
+    }
+
+    public static void main(String[] args) {
+
+        Scanner scanner = new Scanner(System.in);
+        System.out.println("Enter a number");
+        int n = scanner.nextInt();
+        String s = getPrimeSum(n);
+        System.out.println(s);
+    }
+}

src/test/java/com/thealgorithms/maths/GoldbachConjectureTest.java

@@ -0,0 +1,37 @@
+package com.thealgorithms.maths;
+
+import static com.thealgorithms.maths.GoldbachConjecture.getPrimeSum;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class GoldbachConjectureTest {
+    @Test
+    void goldbachTestWithZero() {
+        Assertions.assertEquals("Wrong Input", getPrimeSum(0));
+    }
+    @Test
+    void goldbachTestWithNegative() {
+        Assertions.assertEquals("Wrong Input", getPrimeSum(-50));
+    }
+    @Test
+    void goldbachTestWith2() {
+        Assertions.assertEquals("Wrong Input", getPrimeSum(2));
+    }
+    @Test
+    void goldbachTestWithOdd() {
+        Assertions.assertEquals("Wrong Input", getPrimeSum(25));
+    }
+    @Test
+    void goldbachTestEven1() {
+        Assertions.assertEquals("3 + 5 = 8", getPrimeSum(8));
+    }
+    @Test
+    void goldbachTestEven2() {
+        Assertions.assertEquals("3 + 19 = 22", getPrimeSum(22));
+    }
+    @Test
+    void goldbachTest1() {
+        Assertions.assertEquals("3 + 7 = 10", getPrimeSum(10));
+    }
+}