Key Java Technologies (20) characteristics of parametric types of generics

1.1. characteristics of parameterized types

Parameterized types have the following characteristics:

(1) There is no essential difference between a parameterized type and an original type without a type parameter after compilation.

(2) There are two parameterized types with different type parameters and cannot be mixed.

 Public classGenericparametertest {//parameterized type T, which can be a reference type such as String,integer. Static classSample<t> { //constructor with no arguments.  PublicSample () { This. obj =NULL;} PublicSample (T obj) { This. obj =obj;} //the type of the parameterized type as the return value.  PublicT work () {System.out.println ("Work:" + This. obj);return  This. obj;} //the parameterized type as the type of the parameter.  Public voidupdate (T obj) { This. obj =obj;} //the parameterized type as the type of the property. PrivateT obj;}  Public Static voidMain (string[] args) {//syntax error. Error usage. //sample<int> anothersample = new sample<int> (1);//correct usage. T is an integer.Sample<Integer> anothersample =NewSample<integer> (1); //correct usage: Do not use type parameters, equivalent to sample<string>. //you can now push the export type parameter to string. Sample Sam=NewSample ("Hello"); //error usage, you cannot convert a string to an integer.//Integer result = Sample.work ();//correct usage. String work ();String Result=sample.work ();//The original type.        Equivalent to sample<object> but different from sample<object>. //only the type parameter is inferred as object at this time. Sample SA=NewSample ();//error usage, cannot convert object to string.//String res = sa.work ();//correct usage. Object work ();Object Res=sa.work ();} 

Key Java Technologies (20) characteristics of parametric types of generics