简单理解就是：
司令->传令官->士兵
但是这里隐含了一些东西：
命令是怎样的？
它的基本结构是：
一个抽象的命令接口
一个抽象的命令执行者接口
一个统一调用类
几个具体的命令实现类
几个具体的命令执行者实现类
一个调用者
先看看代码：
抽象的命令执行者接口
public interface Executor {
public void doSomething();
public void doOtherthing();
}
具体的命令执行者实现类
public class ExecutorA implements Executor {
@Override
public void doSomething() {
System.out.println("Executor A do something.");
}
@Override
public void doOtherthing() {
System.out.println("Executor A do otherthing.");
}
}
public class ExecutorB implements Executor {
@Override
public void doSomething() {
System.out.println("Executor B do something.");
}
@Override
public void doOtherthing() {
System.out.println("Executor B other thing.");
}
}
抽象的命令接口
public abstract class Command {
protected Executor executorA = new ExecutorA();
protected Executor executorB = new ExecutorB();
public abstract void execute();
}
具体的命令实现类
public class CommandA extends Command {
@Override
public void execute() {
super.executorA.doSomething();
}
}
public class CommandB extends Command {
@Override
public void execute() {
super.executorB.doOtherthing();
}
}
统一调用类
public class Invoker {
private Command command;
public void setCommand(Command command) {
this.command = command;
}
public void doAction() {
command.execute();
}
}
调用者
public class CommandCaller {
public static void main(String[] args) {
Command ca = new CommandA();
Invoker in = new Invoker();
in.setCommand(ca);
in.doAction();
}
}
那么，如何泛型化呢？显然，Command是入口。泛型化代码如下：
抽象的命令接口
@SuppressWarnings("all")
public abstract class Command<T extends Executor> {
protected T t;
public Command(Class<? extends Executor> c) {
try {
t = (T) Class.forName(c.getName()).newInstance();
} catch (Exception e) {
e.printStackTrace();
}
}
public abstract void execute();
}
具体的命令接口实现类
public class CommandA<T extends Executor> extends Command<T> {
public CommandA(Class<? extends Executor> c) {
super(c);
}
@Override
public void execute() {
super.t.doSomething();
}
}
public class CommandB<T extends Executor> extends Command<T> {
public CommandB(Class<? extends Executor> c) {
super(c);
}
@Override
public void execute() {
super.t.doOtherthing();
}
}
统一调用类
public class Invoker<T extends Command<? extends Executor>> {
private T t;
public void setCommand(T t) {
this.t = t;
}
public void doAction() {
t.execute();
}
}
调用者
public class CommandCaller {
public static void main(String[] args) {
Command<ExecutorA> ca = new CommandA<ExecutorA>(ExecutorA.class);
Invoker<Command<ExecutorA>> in = new Invoker<Command<ExecutorA>>();
in.setCommand(ca);
in.doAction();
}
}