Why Use Generics?为什么使用泛型？

In a nutshell, generics enable types (classes and interfaces) to be parameters when defining classes, interfaces and methods. 简而言之，泛型使类型（类和接口）在定义类、接口和方法时成为参数。Much like the more familiar formal parameters used in method declarations, type parameters provide a way for you to re-use the same code with different inputs. 与方法声明中使用的更为常见的形式参数非常相似，类型参数为您提供了一种方法，可以对不同的输入重复使用相同的代码。The difference is that the inputs to formal parameters are values, while the inputs to type parameters are types.区别在于形式参数的输入是值，而类型参数的输入是类型。

Code that uses generics has many benefits over non-generic code:与非泛型代码相比，使用泛型的代码有许多好处：

• Stronger type checks at compile time.编译时更强的类型检查。
  A Java compiler applies strong type checking to generic code and issues errors if the code violates type safety. Java编译器对泛型代码应用强类型检查，并在代码违反类型安全性时发出错误。Fixing compile-time errors is easier than fixing runtime errors, which can be difficult to find.修复编译时错误比修复运行时错误更容易，因为运行时错误可能很难找到。
  
  
• Elimination of casts.消除强制转换。
  The following code snippet without generics requires casting:以下不带泛型的代码段需要强制转换：

  List list = new ArrayList();
  list.add("hello");
  String s = (String) list.get(0);

  When re-written to use generics, the code does not require casting:当重新编写以使用泛型时，代码不需要强制转换：

  List<String> list = new ArrayList<String>();
  list.add("hello");
  String s = list.get(0);   // no cast

• Enabling programmers to implement generic algorithms.使程序员能够实现通用算法。
  By using generics, programmers can implement generic algorithms that work on collections of different types, can be customized, and are type safe and easier to read.通过使用泛型，程序员可以实现在不同类型的集合上工作、可以自定义、类型安全且易于阅读的泛型算法。