State mode of design mode

Posted by clio-stylers on Sun, 08 Dec 2019 07:21:11 +0100

concept

The behavior of a class changes based on its state

The main idea is to abstract all kinds of concrete state classes. That is, there will be many state classes.

Usage scenarios

Code contains a large number of conditional statements related to object state
Behavior changes with state

Characteristic

States can be transformed from one another, such as workflow.
Each state can complete its own task independently.

Code

Code scenario

At present, there are three statuses for imitating workflow: AState, BState and CState. The flow process of the statuses is AState - > BState - > CState

Specific code

State abstract class AbstractState

/**
 * State abstract class
 * @author GaoYuan
 * @date 2018/11/11 8:42 a.m.
 */
public abstract class AbstractState {

    /** Encapsulates the context */
    protected Context context;

    public void setContext(Context  context){
        this.context = context;
    }

    /** Execution method */
    abstract void run();

    /** Switch to next state */
    abstract void next();
}

Specific status class

public class AState extends AbstractState {

    /** Execution method */
    @Override
    public void run() {
        System.out.println("implement AState Of run() Method");
    }

    /** Switch to next state */
    @Override
    void next() {
        System.out.println("implement AState Of next() Method");
        // The next state defined is BState
        context.setState(new BState());
    }
}
public class BState extends AbstractState {

    /** Execution method */
    @Override
    public void run() {
        System.out.println("implement BState Of run() Method");
    }

    /** Switch to next state */
    @Override
    void next() {
        System.out.println("implement BState Of next() Method");
        // The next state defined is CState
        context.setState(new CState());
    }
}
public class CState extends AbstractState {

    /** Execution method */
    @Override
    public void run() {
        System.out.println("implement CState Of run() Method");
    }

    /** Switch to next state */
    @Override
    void next() {
        System.out.println("implement CState Of next() Method");
        System.out.println("It's the last state!");
    }
}

Context

/**
 * context
 * @author GaoYuan
 * @date 2018/11/11 8:16 a.m.
 */
public class Context {

    private AbstractState state;

    public AbstractState getState() {
        return state;
    }
    /** Set current state */
    public void setState(AbstractState state) {
        this.state = state;
        // Remember setContext, or null pointer
        this.state.setContext(this);
    }
    /** Execution method */
    public void run(){
        this.state.run();
    }
    /** Next state */
    public void next(){
        this.state.next();
    }
}

Test class

/**
 * The flow process of contract status is as state - > bstate - > cstate
 * @author GaoYuan
 * @date 2018/11/11 8:45 a.m.
 */
public class TestMe {

    public static void main(String[] args){
        Context context = new Context();
        context.setState(new AState());

        context.run();
        System.out.println("Current status:" + context.getState().toString());
        context.next();
        System.out.println("Current status:" + context.getState().toString());

        context.run();
        System.out.println("Current status:" + context.getState().toString());
        context.next();
        System.out.println("Current status:" + context.getState().toString());

        context.run();
        System.out.println("Current status:" + context.getState().toString());
        context.next();
        System.out.println("Current status:" + context.getState().toString());

    }
}

output

Execute the run() method of AState
 Current status: com.foruo.learn.designmode.state.AState@2503dbd3
 Execute the next() method of AState
 Current status: com.foruo.learn.designmode.state.BState@4b67cf4d
 Execute the run() method of BState
 Current status: com.foruo.learn.designmode.state.BState@4b67cf4d
 Execute the next() method of BState
 Current status: com.foruo.learn.designmode.state.CState@7ea987ac
 Execute the run() method of CState
 Current status: com.foruo.learn.designmode.state.CState@7ea987ac
 Execute the next() method of CState
 It's the last state!
Current status: com.foruo.learn.designmode.state.CState@7ea987ac