Java泛型自有界类型

Question

考虑下面的示例，避免下面未经检查的转换警告的好方法是什么？ 用户名是

1. 表示通用状态机的接口
2. 每个statemachine实现都需要一个服务，运行相应的状态机时需要一组工具。
3. 一种默认服务，提供跨州机器的公共服务
4. 事务（txn）状态和服务的绑定。

import java.util.function.Consumer;
public class GenericsTest {
  public static void main(String[] args) {
    AService service = new AService("Aservice");
    new Txn<>(service).next();
    new Txn<>(new DefaultState()).next();
  }
}
// ----------------------------------------------------------- //
interface Service {
  String getName();
  <T extends Service> State<T> getState();// this is unclear how to use generics here
}
interface State<T extends Service> {
  Consumer<Txn<T>> getFunction();
  int getN();
}
// ----------------------------------------------------------- //
class Txn<T extends Service> {
  private T service;
  private State<T> current;
  Txn(State<T> current) {
    this.current = current;
  }
  Txn(T service) {
    this.service = service;
    this.current = this.service.getState();
  }
  int next() {
    do {
      current.getFunction().accept(this);
    } while (current.getN()>0);
    return current.getN();
  }
  public State<T> getCurrent() {
    return current;
  }
  public void setCurrent(State<T> current) {
    this.current = current;
  }
}
// ----------------------------------------------------------- //
abstract class DefaultService implements Service {
  private String name;
  public DefaultService(String name) {
    this.name = name;
  }
  public String getName(){
    return this.name.toUpperCase();
  }
}
class AService extends DefaultService implements Service {
  public AService(String name) {
    super(name);
  }
  @Override
  public State<AService> getState() {
    return new AState(6);
  }
}
// ----------------------------------------------------------- //
class DefaultState implements State<DefaultService> {
  @Override
  public Consumer<Txn<DefaultService>> getFunction() {
    return (txn) -> System.out.println("hurray now left is to do default at "+txn.getCurrent().getN());
  }
  @Override
  public int getN() {
    return 0;
  }
}
class AState implements State<AService> {
  private int n;
  AState(int n) {
    this.n = n;
  }
  @Override
  public int getN() {
    return n;
  }
  @Override
  public Consumer<Txn<AService>> getFunction() {
    return (txn) -> {
      int n = txn.getCurrent().getN();
      System.out.println(n);
      txn.setCurrent(new AState(--n));
    };
  }
}

Answer 1

基本上请编程到接口（下面列出的4个更改）：

1. DefaultService已实施Service
2. State<AService>更改为State<Service>
3. class AState implements State<Service>
4. 编程到接口：class Txn<T extends Service> {

更正后的代码：

import java.util.function.Consumer;
public class GenericsTest {
    AService service = new AService("Aservice");
    new Txn<>(service).next();
    new Txn<>(new DefaultState()).next();
  }
}

// ----------------------------------------------------------- //
interface Service {
  String getName();
  <T extends Service> State<T> getState();// this is unclear how to use generics here
}

interface State<T extends Service> {
  Consumer<Txn<T>> getFunction();
  int getN();
}


// ----------------------------------------------------------- //
class Txn<T extends Service> {
  private T service;
  private State<T> current;
  Txn(State<T> current) {
    this.current = current;
  }
  Txn(T service) {
    this.service = service;
    this.current = this.service.getState();
  }
  int next() {
    do {
      current.getFunction().accept(this);
    } while (current.getN()>0);
    return current.getN();
  }
  public State<T> getCurrent() {
    return current;
  }
  public void setCurrent(State<T> current) {
    this.current = current;
  }
}

// ----------------------------------------------------------- //
abstract class DefaultService implements Service {
  private String name;
  public DefaultService(String name) {
    this.name = name;
  }
  public String getName(){
    return this.name.toUpperCase();
  }
}

class AService extends DefaultService {
  public AService(String name) {
    super(name);
  }
  @Override
  public State<Service> getState() {
    return new AState(6);
  }
}

// ----------------------------------------------------------- //
class DefaultState implements State<DefaultService> {
  @Override
  public Consumer<Txn<DefaultService>> getFunction() {
    return (txn) -> System.out.println("hurray now left is to do default at "+txn.getCurrent().getN());
  }
  @Override
  public int getN() {
    return 0;
  }
}

class AState implements State<Service> {
  private int n;
  AState(int n) {
    this.n = n;
  }
  @Override
  public int getN() {
    return n;
  }
  @Override
  public Consumer<Txn<Service>> getFunction() {
    return (txn) -> {
      int n = txn.getCurrent().getN();
      System.out.println(n);
      txn.setCurrent(new AState(--n));
    };
  }
}