Behavioural Design Pattern: State Pattern

The State Pattern is a design pattern that specifies that the behavior of a class is altered based on its current state. The State Pattern involves the creation of objects that represent different states, as well as a context object whose behavior changes depending on the state object.

The State Pattern is alternatively referred to as Objects for States.

Advantages

• It maintains the behavior peculiar to each stage. 
• It explicitly defines all state transitions.

Instructions:

• When an object's behavior is determined by its current state and it has to be able to modify its behavior dynamically based on a new state. 
• This technique is employed when operations involve complex conditional statements that rely on the object's state.

Source code of State.java

package com.t4b.test.java.dp.bp.sp; interface State { public void doAction(Context context); }

Source code of StartState.java

package com.t4b.test.java.dp.bp.sp; class StartState implements State { public void doAction(Context context) { System.out.println("In start state"); context.setState(this); } public String toString() { return "Start State"; } }

Source code of PlayState.java

package com.t4b.test.java.dp.bp.sp; class PlayState implements State { public void doAction(Context context) { System.out.println("In play state"); context.setState(this); } public String toString() { return "Play State"; } }

Source code of StopState.java

package com.t4b.test.java.dp.bp.sp; class StopState implements State { public void doAction(Context context) { System.out.println("In stop state"); context.setState(this); } public String toString() { return "Stop State"; } }

Source code of Context.java

package com.t4b.test.java.dp.bp.sp; class Context { private State state; public Context() { state = null; } public void setState(State state) { this.state = state; } public State getState() { return state; } }

Source code of TestMain.java

package com.t4b.test.java.dp.bp.sp; public class TestMain { public static void main(String[] args) { Context context = new Context(); StartState startState = new StartState(); startState.doAction(context); System.out.println(context.getState().toString()); PlayState playState = new PlayState(); playState.doAction(context); StopState stopState = new StopState(); stopState.doAction(context); System.out.println(context.getState().toString()); } }

Happy Exploring!