什么< T> （尖括号）在Java中是什么意思？ [英] What does <T> (angle brackets) mean in Java?

问题描述

我目前正在学习Java，并且最近被尖括号（<>）难倒了。它们究竟意味着什么？

  public class Pool< T> {
 public interface PoolFactory< T> {
 public T createObject（）; 
} 
 this.freeObjects = new ArrayList< T>（maxsize）
} 
  

< T> 是什么意思？这是否意味着我可以创建一个类型为 T ？

解决方案

< T> 是一个通用，通常可以读作T型。它取决于<>左侧的类型。

我不知道什么是 Pool 或 PoolFactory 是，但是您也提到了 ArrayList< T> ，它是一个标准的Java类，所以我会和你谈谈。

通常，你不会在那里看到T，你会看到另一种类型。因此，例如，如果您看到 ArrayList< Integer> ，那意味着整数的An ArrayList 秒。例如，许多类使用泛型来约束容器中元素的类型。另一个例子是 HashMap< String，Integer> ，这意味着带有字符串键和整数值。

您的Pool示例有点不同，因为您定义了一个类。因此，在这种情况下，您正在创建一个类，其他人可以使用特定类型实例化T。例如，我可以创建一个类型为 Pool< String> 使用你的类定义。这意味着两件事：


• 我的 Pool< String> PoolFactory< String> 带有 createObject 方法返回 String s


• 在内部， Pool< String> 将包含 ArrayList 。
  





这是一个好消息，因为在另一段时间，我可以创建一个 Pool< ;整数> ，它会使用相同的代码，但无论您看到 T ，都有 Integer 在源文件中。

I am currently studying Java and have recently been stumped by angle brackets(<>). What exactly do they mean?

public class Pool<T>{
    public interface PoolFactory<T>{
        public T createObject();
    }
    this.freeObjects= new ArrayList<T>(maxsize)
}

What does the <T> mean? Does it means that I can create an object of type T?

解决方案

<T> is a generic and can usually be read as "of type T". It depends on the type to the left of the <> what it actually means.

I don't know what a Pool or PoolFactory is, but you also mention ArrayList<T>, which is a standard Java class, so I'll talk to that.

Usually, you won't see "T" in there, you'll see another type. So if you see ArrayList<Integer> for example, that means "An ArrayList of Integers." Many classes use generics to constrain the type of the elements in a container, for example. Another example is HashMap<String, Integer>, which means "a map with String keys and Integer values."

Your Pool example is a bit different, because there you are defining a class. So in that case, you are creating a class that somebody else could instantiate with a particular type in place of T. For example, I could create an object of type Pool<String> using your class definition. That would mean two things:

• My Pool<String> would have an interface PoolFactory<String> with a createObject method that returns Strings.
• Internally, the Pool<String> would contain an ArrayList of Strings.

This is great news, because at another time, I could come along and create a Pool<Integer> which would use the same code, but have Integer wherever you see T in the source.

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