BAEL-5132 Abstract class constructors examples (#11389)

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/defaultconstructor/AbstractClass.java

@@ -0,0 +1,5 @@
+package com.baeldung.abstractconstructors.defaultconstructor;
+
+public abstract class AbstractClass {
+    // compiler creates a default constructor
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/defaultconstructor/ConcreteClass.java

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+package com.baeldung.abstractconstructors.defaultconstructor;
+
+public class ConcreteClass extends AbstractClass {
+
+    public ConcreteClass() {
+        super();
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/noargs/AbstractClass.java

@@ -0,0 +1,8 @@
+package com.baeldung.abstractconstructors.noargs;
+
+public abstract class AbstractClass {
+
+    public AbstractClass() {
+        System.out.println("Initializing AbstractClass");
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/noargs/ConcreteClassA.java

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+package com.baeldung.abstractconstructors.noargs;
+
+public class ConcreteClassA extends AbstractClass {
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/noargs/ConcreteClassB.java

@@ -0,0 +1,8 @@
+package com.baeldung.abstractconstructors.noargs;
+
+public class ConcreteClassB extends AbstractClass {
+
+    public ConcreteClassB() {
+        System.out.println("Initializing ConcreteClassB");
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/noargs/Counter.java

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+package com.baeldung.abstractconstructors.noargs;
+
+public abstract class Counter {
+
+    int value;
+
+    private Counter() {
+        this.value = 0;
+        System.out.println("Counter No-Arguments constructor");
+    }
+
+    public Counter(int value) {
+        this.value = value;
+        System.out.println("Parametrized Counter constructor");
+    }
+
+    abstract int increment();
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/noargs/SimpleCounter.java

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+package com.baeldung.abstractconstructors.noargs;
+
+public class SimpleCounter extends Counter {
+
+    public SimpleCounter(int value) {
+        super(value);
+    }
+
+    @Override
+    int increment() {
+        return ++value;
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/parametrized/Car.java

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+package com.baeldung.abstractconstructors.parametrized;
+
+public abstract class Car {
+
+    private int distance;
+
+    private Car(int distance) {
+        this.distance = distance;
+    }
+
+    public Car() {
+        this(0);
+        System.out.println("Car default constructor");
+    }
+
+    abstract String getInformation();
+
+    protected void display() {
+        String info = new StringBuilder(getInformation())
+          .append("\nDistance: " + getDistance())
+          .toString();
+        System.out.println(info);
+    }
+
+    public int getDistance() {
+        return distance;
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/parametrized/ElectricCar.java

@@ -0,0 +1,17 @@
+package com.baeldung.abstractconstructors.parametrized;
+
+public class ElectricCar extends Car {
+
+    int chargingTime;
+
+    public ElectricCar(int chargingTime) {
+        this.chargingTime = chargingTime;
+    }
+
+    @Override
+    String getInformation() {
+        return new StringBuilder("Electric Car")
+          .append("\nCharging Time: " + chargingTime)
+          .toString();
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/main/java/com/baeldung/abstractconstructors/parametrized/FuelCar.java

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+package com.baeldung.abstractconstructors.parametrized;
+
+public class FuelCar extends Car {
+
+    String fuel;
+
+    public FuelCar(String fuel) {
+        this.fuel = fuel;
+    }
+
+    @Override
+    String getInformation() {
+        return new StringBuilder("Fuel Car")
+          .append("\nFuel type: " + fuel)
+          .toString();
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/test/java/com/baeldung/abstractconstructors/noargs/AbstractClassUnitTest.java

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+package com.baeldung.abstractconstructors.noargs;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+class AbstractClassUnitTest {
+
+    @Test
+    void givenNoArgsAbstractConstructor_whenNewSubclassA_thenCalled() {
+        assertNotNull(new ConcreteClassA());
+    }
+
+    @Test
+    void givenNoArgsAbstractConstructor_whenNewSubclassB_thenCalled() {
+        assertNotNull(new ConcreteClassB());
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/test/java/com/baeldung/abstractconstructors/noargs/CounterUnitTest.java

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+package com.baeldung.abstractconstructors.noargs;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+class CounterUnitTest {
+
+    @Test
+    void givenNoArgAbstractConstructor_whenSubclassCreation_thenCalled() {
+        Counter counter = new SimpleCounter(1);
+        assertNotNull(counter);
+        assertEquals(1, counter.value);
+    }
+}

core-java-modules/core-java-lang-oop-constructors/src/test/java/com/baeldung/abstractconstructors/parametrized/CarUnitTest.java

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+package com.baeldung.abstractconstructors.parametrized;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+class CarUnitTest {
+    @Test
+    void givenParametrizedConstructor_whenConcreteCreation_thenCall() {
+        ElectricCar electricCar = new ElectricCar(8);
+        assertNotNull(electricCar);
+        electricCar.display();
+
+        System.out.println();
+
+        FuelCar fuelCar = new FuelCar("Gasoline");
+        assertNotNull(fuelCar);
+        fuelCar.display();
+    }
+}