added command pattern example

src/learn/simple_command/Command.java

@@ -0,0 +1,5 @@
+package learn.simple_command;
+
+public interface Command {
+    void execute();
+}

src/learn/simple_command/ConcreteCommand.java

@@ -0,0 +1,14 @@
+package learn.simple_command;
+
+public class ConcreteCommand implements Command {
+    private Receiver receiver;
+
+    public ConcreteCommand(Receiver receiver) {
+        this.receiver = receiver;
+    }
+
+    @Override
+    public void execute() {
+        receiver.action();
+    }
+}

src/learn/simple_command/Invoker.java

@@ -0,0 +1,13 @@
+package learn.simple_command;
+
+public class Invoker {
+    private Command slot;
+
+    public void setSlot(Command slot) {
+        this.slot = slot;
+    }
+
+    public void buttonWasPushed() {
+        slot.execute();
+    }
+}

src/learn/simple_command/Main.java

@@ -0,0 +1,12 @@
+package learn.simple_command;
+
+public class Main {
+    public static void main(String[] args) {
+        Invoker invoker = new Invoker();
+        Receiver receiver = new Receiver();
+        Command command = new ConcreteCommand(receiver);
+        invoker.setSlot(command);
+
+        invoker.buttonWasPushed();
+    }
+}

src/learn/simple_command/Receiver.java

@@ -0,0 +1,7 @@
+package learn.simple_command;
+
+public class Receiver {
+    public void action() {
+        System.out.println("Do my action");
+    }
+}