BAEL-2836 Mediator Pattern in Java

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Button.java

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+package com.baeldung.mediator;
+
+public class Button {
+    private Mediator mediator;
+
+    public void setMediator(Mediator mediator) {
+        this.mediator = mediator;
+    }
+
+    public void press() {
+        this.mediator.press();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Fan.java

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+package com.baeldung.mediator;
+
+public class Fan {
+    private Mediator mediator;
+    private boolean isOn = false;
+
+    public void setMediator(Mediator mediator) {
+        this.mediator = mediator;
+    }
+
+    public boolean isOn() {
+        return isOn;
+    }
+
+    public void turnOn() {
+        this.mediator.start();
+        isOn = true;
+    }
+
+    public void turnOff() {
+        isOn = false;
+        this.mediator.stop();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/Mediator.java

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+package com.baeldung.mediator;
+
+public class Mediator {
+    private Button button;
+    private Fan fan;
+    private PowerSupplier powerSupplier;
+
+    public void setButton(Button button) {
+        this.button = button;
+        this.button.setMediator(this);
+    }
+
+    public void setFan(Fan fan) {
+        this.fan = fan;
+        this.fan.setMediator(this);
+    }
+
+    public void setPowerSupplier(PowerSupplier powerSupplier) {
+        this.powerSupplier = powerSupplier;
+    }
+
+    public void press() {
+        if (fan.isOn()) {
+            fan.turnOff();
+        } else {
+            fan.turnOn();
+        }
+    }
+
+    public void start() {
+        powerSupplier.turnOn();
+    }
+
+    public void stop() {
+        powerSupplier.turnOff();
+    }
+}

patterns/design-patterns-2/src/main/java/com/baeldung/mediator/PowerSupplier.java

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+package com.baeldung.mediator;
+
+public class PowerSupplier {
+    public void turnOn() {
+        // implementation
+    }
+
+    public void turnOff() {
+        // implementation
+    }
+}

patterns/design-patterns-2/src/test/java/com/baeldung/mediator/ButtonTest.java

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+package com.baeldung.mediator;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class ButtonTest {
+
+    private Button button;
+    private Fan fan;
+
+    @Before
+    public void setUp() {
+        this.button = new Button();
+        this.fan = new Fan();
+        PowerSupplier powerSupplier = new PowerSupplier();
+        Mediator mediator = new Mediator();
+
+        mediator.setButton(this.button);
+        mediator.setFan(fan);
+        mediator.setPowerSupplier(powerSupplier);
+    }
+
+    @Test
+    public void givenTurnedOffFan_whenPressingButtonTwice_fanShouldTurnOnAndOff() {
+        assertFalse(fan.isOn());
+
+        button.press();
+        assertTrue(fan.isOn());
+
+        button.press();
+        assertFalse(fan.isOn());
+    }
+}