1. State mode

1.1 State Patterns - Core Ideas

1.2 State Patterns-Class Diagrams

The state model has three main roles:

• State: An abstract state role that defines state-related behavior. Context can be used as a parameter of a method.
• ConcreteState: Specific state, which implements different ways of behaving in that state
• Context: Environment role, maintenance of a State instance, support for state modification

1.4 State Patterns - Advantages and Disadvantages

• Advantage:
  • Clear structure, avoiding excessive if-else, switch-case structure
  • Following the principle of single responsibility and the principle of opening and closing
  • Good encapsulation
• Disadvantages:
  • Increasing state classes increases the number and type of classes in the system
  • The structure and implementation of state mode are complex, and improper use will lead to confusion of program structure and code.

1.5 state mode - applicable scenario

• Scenarios in which behavior changes with state
• Conditions, Substitutes for Branch Judgment Statements

2. State Patterns - Examples of Applications

Class 2.1 Graphs

2.2 Elevator State Interface-ILiftState

Abstract elevator door opening and closing method

public interface ILiftState {

    public void open();

    public void close();
}

2.2 Running State-LiftRunState

public class LiftRunState implements ILiftState {
    @Override
    public void open() {
        System.out.println("Elevator runs regularly and cannot open the door");
    }

    @Override
    public void close() {
        System.out.println("Elevator runs regularly and cannot close elevator door");
    }
}

2.2 Stop State - LiftStop State

public class LiftStopState implements ILiftState {
    @Override
    public void open() {
        System.out.println("Open the elevator door...");
    }

    @Override
    public void close() {
        System.out.println("Close the elevator door...");
    }
}

2.2 Elevator Class - ILiftState

public class Lift {

    private ILiftState liftState;

    public ILiftState getLiftState() {
        return liftState;
    }

    public void setLiftState(ILiftState liftState) {
        this.liftState = liftState;
    }

    public void openDoor() {
        this.liftState.open();
    }

    public void closeDoor(){
        this.liftState.close();
    }
}

2.2 Test

Setting up different states will result in different outputs

@Test
public void test_state(){

    Lift lift = new Lift();
    lift.setLiftState(new LiftRunState());

    lift.openDoor();
    lift.closeDoor();
}

3. Contrast

If you don't use state mode, the code is probably written like this

public class Liftt {

    // running state
    public static final int STATE_RUN = 1;

    // Suspension status
    public static final int STATE_STOP = 0;

    private int liftState;

    public int getLiftState() {
        return liftState;
    }

    public void setLiftState(int liftState) {
        this.liftState = liftState;
    }

    public void close(){
        switch (liftState) {
            case STATE_RUN:
                System.out.println("The elevator is running and the door is closed.");
                break;
            case STATE_STOP:
                System.out.println("Close the elevator door");
                break;
        }
    }

    public void open() {
        switch (liftState) {
            case STATE_RUN:
                System.out.println("The elevator is running and cannot be opened.");
                break;
            case STATE_STOP:
                System.out.println("Open the elevator door");
                break;
        }
    }

}