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Design Patterns in Java (Creational) - State Pattern

State Pattern


  • Localize state behavior
  • Separate what from where




Main
public static void main(String[] args) {
Fan fan = new Fan();
System.out.println(fan);

fan.pullChain();
System.out.println(fan);
fan.pullChain();

System.out.println(fan);
}

Fan

public class Fan {
State fanOff;
State fanLow;
State fanMedium;
State currentState;
public Fan(){
fanOff = new FanOff(this);
fanLow = new FanLow(this);
fanMedium = new FanMedium(this);
currentState = fanOff;
}
public void setState(State state){
currentState = state;
}
public State getLowState(){
return fanLow;
}
public State getMediumState(){
return fanMedium;
}
public State getOffState(){
return fanOff;
}
public void pullChain(){
currentState.handleRequest();
}
public String toString(){
return currentState.toString();
}
}

State

public abstract class State {
public void handleRequest(){
System.out.println("Action not established");
}
}

FanOff

public class FanOff extends State {
Fan fan;
public FanOff(Fan fan) {
this.fan = fan;
}

@Override
public void handleRequest(){
System.out.println("Turning fan on to low");
fan.setState(fan.getLowState());
}
public String toString(){
return "Fan is off";
}
}


FanLow

public class FanLow extends State {
Fan fan;

public FanLow(Fan fan) {
this.fan = fan;
}

@Override
public void handleRequest(){
System.out.println("From low to medium");
fan.setState(fan.getMediumState());
}

public String toString(){
return "Fan is low";
}
}


FanMedium

public class FanMedium extends State {
Fan fan;

public FanMedium(Fan fan) {
this.fan = fan;
}

@Override
public void handleRequest() {
System.out.println("From medium to off state");
fan.setState(fan.getOffState());
}

public String toString(){
return "Fan is in medium";
}
}











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