We need to create validators for each status. The validator will check if transition from current state is allowed or not.

public class Order {
    public enum State {
        PENDING,
        SUSPENDED,
        ACTIVE,
        CANCELLED,
        COMPLETED
    }

    Status state;

    public Order() {
        this.state = State.PENDING;
    }

    public void approve() {
        if (this.state == State.PENDING) {
            this.state = State.ACTIVE;
        }
    }

    public void suspend() {
        if (this.state == State.ACTIVE) {
            this.state = State.SUSPENDED;
        }
    }

    public void complete() {
        if (this.state == State.ACTIVE || this.state == State.SUSPENDED) {
            this.state = State.COMPLETED;
        }
    }

    public void cancel() {
        if (this.state == State.ACTIVE || this.state == State.PENDING) {
            this.state = State.CANCELLED;
        }
    }

    public