UML类图

UML：统一建模语言

UML类图，嗯，设计模式上看到的，挺好的，可以很好地帮助人思考问题。

GoF-Behavioral Design Patterns:State Pattern(状态模式)

abstract class State
{
 public void pull( Car wrapper )
 {
  wrapper.setState( new Off() );
  System.out.println( " turning off" );
 }
}
class Car
{
 private State current;
 public Car()
 {
  current = new Off();
  System.out.println("A new car has came out,now it's off!");
 }
 public void setState( State s )
 {
  current = s;
 }
 public void pull()
 {
  current.pull( this );
 }
}

class Off extends State
{
 public void pull( Car wrapper )
 {
  wrapper.setState( new Low() );
  System.out.println( "Low speed!" );
 }
}

class Low extends State
{
 public void pull( Car wrapper )
 {
  wrapper.setState( new High() );
  System.out.println( "High speed!" );
 }
}

class High extends State
{
 public void pull( Car wrapper )
 {
  wrapper.setState( new Off() );
  System.out.println( "Off speed!" );
 }
}

class Client
{
 public static void main(String[] args)
 {
  Car car = new Car();
  car.pull();
  car.pull();
  car.pull();
 }
}