Java未绑定的通配符泛型 [英] Java unbound wildcard generics

问题描述

在 Bar 类中使用通配符类型的优点是否完全忽略它们？

  public class Foo< T> {} 
 
 public interface Bar {
 public void addFoo（Foo<？> foo）; 
 public Foo<？> getFoo（String name）; 
 
  

解决方案

有很多优点。 / p>

• 它们不会像使用原始类型那样产生编译器警告



• 更多的类型安全。例如，考虑 Foo 是不是 List 。如果您使用 List 而不是 List <？>< / code>，您可以这样做：

    myBar.getFoo（numbers）。add（some string）; 
    

  即使列表只有假设包含数秒。如果您返回了 List<？> ，那么您将无法向其添加任何内容（除 null



• 它们记录与原始类型完全不同的内容，即 Foo 在某些未知但特定类型上键入。
  

Are there any advantages of using wildcard-type generics in the Bar class over completely skipping them?

public class Foo<T> {}

public interface Bar {
    public void addFoo(Foo<?> foo);
    public Foo<?> getFoo(String name);
}

解决方案

There are multiple advantages.

• They won't produce compiler warnings like using the raw type would

• They give more type safety. For example, consider if Foo was List instead. If you used List instead of List<?>, you could do this:

  myBar.getFoo("numbers").add("some string");
  

  even if the list was only supposed to contain Numbers. If you returned a List<?>, then you would not be able to add anything to it (except null) since the type of list is not known.

• They document something completely different than a raw type, namely that Foo is typed on some unknown but specific type.

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