Question

对贾瓦来说,情况相对较新,我最近走过了我以前从未见过的yn。

public class loadSomeData extends AsyncTask<String, Integer, String>{ etc..}

The part that confuses me is the stuff between the <> brackets. I understand what each of the Types are used for in this class, but why declare them in the class declaration?

更具体地说,这一点是什么:<DataType>,在 Java呼吁,以便我研究?

谢谢。

Answer 1

http://en.wikipedia.org/wiki/Generics_in_Java"rel=“nofollow” in Java。

In brief, a collection class (or any class, really) may declare a parameterized type using that syntax so that users of the class can ensure that only objects of the same type will be stored in its collections (or otherwise operated on by it).

在非专利之前,在清单等收集方面没有任何类型安全:

List numbers = new ArrayList();
numbers.add(Integer.valueOf(123)); // OK
numbers.add("foo"); // Uh-oh!

但现在,你可以确保,只有你宣布的类型才能增加:

List<Number> numbers = new ArrayList<Number>();
numbers.add(Integer.valueOf(123)); // OK
numbers.add("foo"); // Compile-time error!

Answer 2

你们正在看到 Java的基因特征。 http://docs.oracle.com/javase/tutorial/java/generics/index.html” rel=“nofollow” http://docs.oracle.com/javase/tutorial/java/generics/index.html。

Answer 3

The <DataType> structure is referred to as category paramaters of the 缩略语 Java类。这意味着在其运作中可以使用不同的通用类别。见上文链接。

Answer 4

AsyncTask 是generic 类型,因为其参数可与java.util一样。 List ,java.util. Set 和许多标准 Java班。

阅读 to Learning more.

在班级申报中申报这些内容是有益的,因为装载SomeData(应称LoadSomeData,甚至更名为:Vata Loader)是处理强硬、煽动和强硬的AyncTask的专业化,而不是任何其他类型。

友情链接