State Pattern

Structure

Code Examples

Simple Example

interface State {
    void handle();
}

class OnState implements State {
    public void handle() { System.out.println("Turning ON"); }
}

class OffState implements State {
    public void handle() { System.out.println("Turning OFF"); }
}

class Context {
    private State state;
    public void setState(State state) { this.state = state; }
    public void request() { state.handle(); }
}

// Usage
Context ctx = new Context();
ctx.setState(new OnState());
ctx.request(); // "Turning ON"
ctx.setState(new OffState());
ctx.request(); // "Turning OFF"

Comparisons

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Strategy Pattern vs State Pattern

• in State Pattern, particular states are aware of each other
• in Strategy Pattern, strategies are almost never aware of each other

Link to original

Resources

• https://refactoring.guru/design-patterns/state