Sample of Java Pattern -- State

OrderState.java

package state;

public interface OrderState {
    public void handleOrder(String orderNo);
    public void cancelOrder(String orderNo);
    public void completeOrder(String orderNo);
}

OrderOpendState.java

package state;

public class OrderOpendState implements OrderState {
    
    OrderStateMgmt orderStateMgmt;
    
    public OrderOpendState(OrderStateMgmt orderStateMgmt){
        this.orderStateMgmt = orderStateMgmt;
    }
    
    public void handleOrder(String orderNo){
        System.out.println("handle this order, orderNo=" + orderNo);
        orderStateMgmt.setState(orderStateMgmt.getOrderInProgressState());
    }
    
    public void cancelOrder(String orderNo){
        System.out.println("cancel this order, orderNo=" + orderNo);
        orderStateMgmt.setState(orderStateMgmt.getOrderCancelledState());
    }
    
    public void completeOrder(String orderNo){
        System.out.println("could not complete this order under opend status, orderNo=" + orderNo);
    }
}

OrderInProgressState.java

package state;

public class OrderInProgressState implements OrderState {
    
    OrderStateMgmt orderStateMgmt;
    
    public OrderInProgressState(OrderStateMgmt orderStateMgmt){
        this.orderStateMgmt = orderStateMgmt;
    }
    
    public void handleOrder(String orderNo){
        System.out.println("could not handle this order under in progress status, orderNo=" + orderNo);
    }
    
    public void cancelOrder(String orderNo){
        System.out.println("cancel this order, orderNo=" + orderNo);
        orderStateMgmt.setState(orderStateMgmt.getOrderCancelledState());
    }
    
    public void completeOrder(String orderNo){
        System.out.println("complete this order, orderNo=" + orderNo);
        orderStateMgmt.setState(orderStateMgmt.getOrderClosedState());
    }
}

OrderCancelledState.java

package state;

public class OrderCancelledState implements OrderState {
    
    OrderStateMgmt orderStateMgmt;
    
    public OrderCancelledState(OrderStateMgmt orderStateMgmt){
        this.orderStateMgmt = orderStateMgmt;
    }
    
    public void handleOrder(String orderNo){
        System.out.println("could not handle this order under cancelled status, orderNo=" + orderNo);
    }
    
    public void cancelOrder(String orderNo){
        System.out.println("could not cancel this order under cancelled status, orderNo=" + orderNo);
    }
    
    public void completeOrder(String orderNo){
        System.out.println("could not complete this order under cancelled status, orderNo=" + orderNo);
    }
}

OrderClosedState.java

package state;

public class OrderClosedState implements OrderState {
    
    OrderStateMgmt orderStateMgmt;
    
    public OrderClosedState(OrderStateMgmt orderStateMgmt){
        this.orderStateMgmt = orderStateMgmt;
    }
    
    public void handleOrder(String orderNo){
        System.out.println("could not handle this order under closed status, orderNo=" + orderNo);
    }
    
    public void cancelOrder(String orderNo){
        System.out.println("could not cancel this order under closed status, orderNo=" + orderNo);
    }
    
    public void completeOrder(String orderNo){
        System.out.println("could not complete this order under closed status, orderNo=" + orderNo);
    }
}

OrderStateMgmt.java

package state;

public class OrderStateMgmt {
    
    private OrderOpendState orderOpendState;
    private OrderInProgressState orderInProgressState;
    private OrderCancelledState orderCancelledState;
    private OrderClosedState orderClosedState;
    
    private OrderState orderState;
    
    public OrderStateMgmt(){
        this.orderOpendState = new OrderOpendState(this);
        this.orderInProgressState = new OrderInProgressState(this);
        this.orderCancelledState = new OrderCancelledState(this);
        this.orderClosedState = new OrderClosedState(this);
        this.orderState = this.orderOpendState;
        System.out.println("The order inital status is: opend.");
    }
    
    public void setState(OrderState orderState){
        this.orderState = orderState;
    }

    public OrderOpendState getOrderOpendState() {
        return orderOpendState;
    }

    public OrderInProgressState getOrderInProgressState() {
        return orderInProgressState;
    }

    public OrderCancelledState getOrderCancelledState() {
        return orderCancelledState;
    }

    public OrderClosedState getOrderClosedState() {
        return orderClosedState;
    }

    public void handleOrder(String orderNo){
        orderState.handleOrder(orderNo);
    }
    
    public void cancelOrder(String orderNo){
        orderState.cancelOrder(orderNo);
    }
    
    public void completeOrder(String orderNo){
        orderState.completeOrder(orderNo);
    }
}

OrderStateTest.java

package state;

public class OrderStateTest {

    public static void main(String[] args) {
        OrderStateMgmt orderStateMgmtA = new OrderStateMgmt();
        
        orderStateMgmtA.handleOrder("01");
        orderStateMgmtA.completeOrder("01");

        OrderStateMgmt orderStateMgmtB = new OrderStateMgmt();

        orderStateMgmtB.handleOrder("02");
        orderStateMgmtB.cancelOrder("02");
        
        OrderStateMgmt orderStateMgmtC = new OrderStateMgmt();

        orderStateMgmtC.completeOrder("03");
    }

}

you may download the source code.