Java Interfaces Examples (#5992)

* Implementing Hexagonal Architecture in java

* Implementing multi-inheritance and Polymorphism using interfaces

* Removing hexagonal code

* Deleting hexagonal architecture code

* fix for unit test names

* Java Interfaces examples

core-java-8/src/main/java/com/baeldung/interfaces/Electronic.java

@@ -0,0 +1,22 @@
+package com.baeldung.interfaces;
+
+public interface Electronic {
+    //Constant variable
+    public static final String LED = "LED";
+
+    //Abstract method
+    public int getElectricityUse();
+
+    // Static method
+    public static boolean isEnergyEfficient(String electtronicType) {
+        if (electtronicType.equals(LED)) {
+            return true;
+        }
+        return false;
+    }
+
+    //Default method
+    public default void printDescription() {
+        System.out.println("Electronic Description");
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/Employee.java

@@ -0,0 +1,15 @@
+package com.baeldung.interfaces;
+
+public class Employee {
+
+    private double salary;
+
+    public double getSalary() {
+        return salary;
+    }
+
+    public void setSalary(double salary) {
+        this.salary = salary;
+    }
+
+}

core-java-8/src/main/java/com/baeldung/interfaces/EmployeeSalaryComparator.java

@@ -0,0 +1,18 @@
+package com.baeldung.interfaces;
+
+import java.util.Comparator;
+
+public class EmployeeSalaryComparator implements Comparator<Employee> {
+
+    @Override
+    public int compare(Employee employeeA, Employee employeeB) {
+
+        if(employeeA.getSalary() < employeeB.getSalary()){
+            return -1;
+        }else if(employeeA.getSalary() > employeeB.getSalary()){
+            return 1;
+        }else{
+            return 0;
+        }
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/HasColor.java

@@ -0,0 +1,5 @@
+package com.baeldung.interfaces;
+
+public interface HasColor {
+    public String getColor();
+}

core-java-8/src/main/java/com/baeldung/interfaces/Motorcycle.java

@@ -0,0 +1,10 @@
+package com.baeldung.interfaces;
+
+import com.baeldung.interfaces.multiinheritance.Transform;
+
+public class Motorcycle implements Transform {
+    @Override
+    public void transform() {
+        // Implementation
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/Truck.java

@@ -0,0 +1,8 @@
+package com.baeldung.interfaces;
+
+public class Truck extends Vehicle {
+    @Override
+    public void transform() {
+        // implementation
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/Vehicle.java

@@ -0,0 +1,6 @@
+package com.baeldung.interfaces;
+
+import com.baeldung.interfaces.multiinheritance.Transform;
+
+public abstract class Vehicle implements Transform {
+}

core-java-8/src/main/java/com/baeldung/interfaces/multiinheritance/Car.java

@@ -0,0 +1,13 @@
+package com.baeldung.interfaces.multiinheritance;
+
+public class Car implements Fly, Transform {
+    @Override
+    public void fly() {
+        System.out.println("I can Fly!!");
+    }
+
+    @Override
+    public void transform() {
+        System.out.println("I can Transform!!");
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/multiinheritance/Transform.java

@@ -1,5 +1,10 @@
 package com.baeldung.interfaces.multiinheritance;
 
 public interface Transform {
+
     void transform();
+
+    default void printSpecs(){
+        System.out.println("Transform Specification");
+    }
 }

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Circle.java

@@ -18,4 +18,8 @@ public class Circle implements Shape {
         return Math.PI * (radius * radius);
     }
 
+    @Override
+    public String getColor() {
+        return "green";
+    }
 }

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/DisplayShape.java

@@ -6,6 +6,10 @@ public class DisplayShape {
 
     private ArrayList<Shape> shapes;
 
+    public ArrayList<Shape> getShapes() {
+        return shapes;
+    }
+
     public DisplayShape() {
         shapes = new ArrayList<>();
     }

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/FunctionalMain.java

@@ -0,0 +1,23 @@
+package com.baeldung.interfaces.polymorphysim;
+
+import java.util.function.Predicate;
+
+public class FunctionalMain {
+
+public static void main(String[] args) {
+    Shape circleShape = new Circle(2);
+    Shape squareShape = new Square(2);
+
+    DisplayShape DisplayShape = new DisplayShape();
+    DisplayShape.add(circleShape);
+    DisplayShape.add(squareShape);
+
+    Predicate<Shape> checkArea = (shape) -> shape.area() < 5;
+
+    for (Shape shape : DisplayShape.getShapes()) {
+        if (checkArea.test(shape)) {
+            System.out.println(shape.name() + " " + shape.area());
+        }
+    }
+}
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Shape.java

@@ -1,6 +1,9 @@
 package com.baeldung.interfaces.polymorphysim;
 
-public interface Shape {
+import com.baeldung.interfaces.HasColor;
+
+public interface Shape extends HasColor {
+
     public abstract String name();
     public abstract double area();
 }

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Square.java

@@ -17,4 +17,9 @@ public class Square implements Shape {
     public double area() {
         return width * width;
     }
+
+    @Override
+    public String getColor() {
+        return "red";
+    }
 }