classes and objects code added (#6173)

* classes and objects code added

* Car class and test added

* fixes and enhancements

* code moved to core-java-lang

core-java-lang/src/main/java/com/baeldung/objects/Car.java

@@ -0,0 +1,51 @@
+package com.baeldung.objects;
+
+public class Car {
+
+    private String type;
+    private String model;
+    private String color;
+    private int speed;
+
+    public Car(String type, String model, String color) {
+        this.type = type;
+        this.model = model;
+        this.color = color;
+    }
+
+    public String getColor() {
+        return color;
+    }
+
+    public void setColor(String color) {
+        this.color = color;
+    }
+
+    public int getSpeed() {
+        return speed;
+    }
+    
+    public int increaseSpeed(int increment) {
+        if (increment > 0) {
+            this.speed += increment;
+        } else {
+            System.out.println("Increment can't be negative.");
+        }
+        return this.speed;
+    }
+    
+    public int decreaseSpeed(int decrement) {
+        if (decrement > 0 && decrement <= this.speed) {
+            this.speed -= decrement;
+        } else {
+            System.out.println("Decrement can't be negative or greater than current speed.");
+        }
+        return this.speed;
+    }
+
+    @Override
+    public String toString() {
+        return "Car [type=" + type + ", model=" + model + ", color=" + color + ", speed=" + speed + "]";
+    }
+    
+}

core-java-lang/src/test/java/com/baeldung/objects/CarUnitTest.java

@@ -0,0 +1,38 @@
+package com.baeldung.objects;
+
+import static org.junit.Assert.*;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class CarUnitTest {
+    
+    private Car car;
+
+    @Before
+    public void setUp() throws Exception {
+        car = new Car("Ford", "Focus", "red");
+    }
+
+    @Test
+    public final void when_speedIncreased_then_verifySpeed() {
+        car.increaseSpeed(30);
+        assertEquals(30, car.getSpeed());
+        
+        car.increaseSpeed(20);
+        assertEquals(50, car.getSpeed());
+    }
+    
+    @Test
+    public final void when_speedDecreased_then_verifySpeed() {
+        car.increaseSpeed(50);
+        assertEquals(50, car.getSpeed());
+        
+        car.decreaseSpeed(30);
+        assertEquals(20, car.getSpeed());
+        
+        car.decreaseSpeed(20);
+        assertEquals(0, car.getSpeed());
+    }
+
+}