BAEL-870 How to call a method during runtime using reflection? (#1769)

* BAEL 870 How to call method during runtime using reflection?

* BAEL-870 How to call a method during runtime using reflection?

core-java/src/main/java/com/baeldung/java/reflection/Operations.java

@@ -0,0 +1,17 @@
+package com.baeldung.java.reflection;
+
+public class Operations {
+    
+    public double sum(int a, double b) {
+        return a + b;
+    }
+    
+    public static double multiply(float a, long b){
+        return a * b;
+    }
+
+    private boolean and(boolean a, boolean b) {
+        return a && b;
+    }
+    
+}

core-java/src/test/java/com/baeldung/java/reflection/OperationsUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.java.reflection;
+
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import org.testng.Assert;
+import org.testng.annotations.Test;
+
+public class OperationsUnitTest {
+
+    public OperationsUnitTest() {
+    }
+
+    @Test(expectedExceptions = IllegalAccessException.class)
+    public void givenObject_whenInvokePrivatedMethod_thenFail() throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException{
+        Method andInstanceMethod = Operations.class.getDeclaredMethod("and", boolean.class, boolean.class);
+
+        Operations operationsInstance = new Operations();
+        Boolean result = (Boolean)andInstanceMethod.invoke(operationsInstance, true, false);
+
+        Assert.assertFalse(result);
+    }
+
+    @Test
+    public void givenObject_whenInvokePrivateMethod_thenCorrect() throws Exception {
+        Method andInstanceMethod = Operations.class.getDeclaredMethod("and", boolean.class, boolean.class);
+        andInstanceMethod.setAccessible(true);
+
+        Operations operationsInstance = new Operations();
+        Boolean result = (Boolean)andInstanceMethod.invoke(operationsInstance, true, false);
+
+        Assert.assertFalse(result);
+    }
+
+    @Test
+    public void givenObject_whenInvokePublicMethod_thenCorrect() throws Exception {
+        Method sumInstanceMethod = Operations.class.getMethod("sum", int.class, double.class);
+
+        Operations operationsInstance = new Operations();
+        Double result = (Double)sumInstanceMethod.invoke(operationsInstance, 1, 3);
+        
+        Assert.assertTrue(4 == result);
+    }
+    
+    @Test
+    public void givenObject_whenInvokeStaticMethod_thenCorrect() throws Exception {
+        Method multiplyStaticMethod = Operations.class.getDeclaredMethod("multiply",float.class, long.class);
+
+        Double result = (Double)multiplyStaticMethod.invoke(null, 3.5f, 2);
+        
+        Assert.assertTrue(7 == result);
+    }
+
+}