/ Design Patterns / Behavioral patterns / State

State Design Pattern in Java

State design pattern implementation

abstract class State {
    public void pull(Chain wrapper) {
        wrapper.setState(new Off());
        System.out.println("   turning off");
    }
}

class Chain {
    private State current;

    public Chain() {
        current = new Off();
    }

    public void setState(State state) {
        current = state;
    }

    public void pull() {
        current.pull(this);
    }
}

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

class Low extends State {
    public void pull(Chain wrapper) {
        wrapper.setState(new Medium());
        System.out.println("   medium speed");
    }
}

class Medium extends State {
    public void pull(Chain wrapper) {
        wrapper.setState(new High());
        System.out.println("   high speed");
    }
}

class High extends State { }

public class StateDemo {
    public static void main( String[] args ) throws IOException {
        InputStreamReader is = new InputStreamReader( System.in );
        Chain chain = new Chain();
        while (true) {
            System.out.print( "Press 'Enter'" );
            is.read();
            chain.pull();
        }
    }
}

Output

Press 'Enter'
   low speed
Press 'Enter'
   medium speed
Press 'Enter'
   high speed
Press 'Enter'
   turning off
Press 'Enter'
   low speed
Press 'Enter'
   medium speed
Press 'Enter'
   high speed
Press 'Enter'
   turning off

Code examples

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