Java语法大于/小于：<>他们是特定类别的吗？ [英] Java syntax with greater than/less than: <> are they class specific?

问题描述

  public class ImageAndTextAdapter extends ArrayAdapter< String> ; {
  

< String> a按类型继承的形式？或者是我应该知道的其他一些Java语法？

该类为：

  android.widget.ArrayAdapter<字符串> 
  

解决方案

这就是所谓的泛型 。 < 和> 中的类是类型参数。

这可以通过一个例子来解释：
$ b ArrayList can存储物品。如果你指定了这样的类型参数： ArrayList< String> ，那么这个数组列表将存储字符串类型的项（换句话说，它将仅存储 String s）！

同样， ArrayAdapter 也由一个类型参数化。 ArrayAdapter 可能包含一个值，该值将是< 和<$ c $之间指定的类型c>> ，这在你的情况下是字符串。

有用的链接：

• 泛型的官方追踪（一个好的起点）

I've been doing an Android tutorial and encountered a class with the following:

public class ImageAndTextAdapter extends ArrayAdapter<String> {

Is the <String> a form of inheritance by type? Or is it some other Java syntax that I should know about?

The class is:

android.widget.ArrayAdapter<String>

解决方案

This is called generics. The class within < and > is a type parameter.

This is easiest explained by an example:

An ArrayList can store items. If you specify a type parameter like this: ArrayList<String> then this array list will store items of String type only, (in other words, it will store Strings only)!

Similarly, the ArrayAdapter is "parameterized" by a type as well. The ArrayAdapter probably holds a value, and this value will be of the type specified between < and >, which in your case is String.

Useful links:

• Official trail on Generics (a good starting point)

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