类型参数E隐藏类型E.泛型模板到一个类 [英] The type parameter E is hiding the type E. Generics template to a class

问题描述

我正在练习仿制药，我做了以下事情.

I am practicing generics and i did the following.

创建了一个名为man的类，如下所示.

Created a class called man as below.

public class Man{
int hands=2;
int legs=2;
boolean alive;

public Man(boolean b) {
    // TODO Auto-generated constructor stub
    alive=b;
}

}

创建了一个名为人"的课程

created a class called person

public class Person<Man> {
Man p;
String name;


public Person(Man p, String name) {
    this.p = p;
    this.name = name;
}
public Person() {
    // TODO Auto-generated constructor stub
}

}

试图实例化如下所示的string或int类型的人，并且它抛出错误.

tried to instantiate a person of type string or int as below and it dosent throw an error.

Person<String> p1 = new Person<String>(new String("test"), "test1");
    Person<Integer> p2=new Person<>(1,"test");

当我仔细检查时，收到以下警告.类型参数Man正在隐藏类型Man"

when i checked carefully, i got the following warning. "The type parameter Man is hiding the type Man"

所以我知道在类Java例子中给Man作为类Person的类型参数与给'E'一样好.它不是Man.class.为什么会这样呢?如何将我的Man.class分配为通用类型参数?

So i understand that giving Man as a type parameter to the class Person is as good as giving 'E' in java examples. Its not Man.class. Why did this happen? How do i assign my Man.class as the generic type parameter?

您能给我扔一些好的问题/练习来学习泛型吗?

and can you throw me some good questions/practice exercises to learn generics.

推荐答案

因为 Man 是同一包中的类的名称.只需将通用名称从 Person< Man> 更改为 Person< T> 或其他与 Man 都不相似的名称即可其他班级.

Because Man is the name of a class in the same package. Just change the name of your generic from Person<Man> to Person<T> or something else that doesn't resemble nor Man nor any other class.

有关泛型的更多信息:

• Java教程.课程:泛型(已更新)

看起来您希望 Person 使用泛型仅具有 Man 属性.您将需要具有一个定义通用类的超类，并且 Person 将从其继承，以定义它使用 Man 作为所使用的类.简短示例:

Looks like you want that Person has only Man attribute using generics. You will need for that to have a super class that defines the generic and Person will inherit from it defining that it uses Man as the class used. Short example:

public abstract class AliveBeing<T> {
    protected T livingBeing;
    public AliveBeing(T livingBeing) {
        this.livingBeing = livingBeing;
    }
}

public class Person extends AliveBeing<Man> {
    //now your livingBeing field is from Man type...
    public Person(Man man) {
        super(man);
    }
}

这可以做到，但IMO的这种设计很奇怪.最好多解释一下您当前的问题，以获得更好，更准确的答案.

This will make it but IMO this design is odd. It would be better to explain more about your current problem to get a better and accurate answer.

请注意区别:

//case 1
public class Foo<T> {
    //...
}

//case 2
public class Bar<E> extends Foo<E> {
    //...
}

//case 3
public class Baz extends Foo<String> {
    //...
}

在第一种情况下， Foo 使用泛型类，您可以通过 T 引用此类.在第二种情况下， Bar 是 Foo 的扩展，并使用其自己的泛型类进行声明，您可以通过 E 引用它，但是此E 将与 Foo 中使用的泛型相同(而不是 T ，它将是 E ).在第三种情况下， Baz 类从 Foo 扩展而来，但是它没有定义任何通用行为，而是声明了 Foo 中使用的通用类.是 String .

In first case, Foo uses a generic class and you can refer to this class by T. In second case, Bar extends from Foo and declares using its own generic class and you can refer to it by E, but this E will be the same generic used from Foo (instead of T it will be E). In third case, Baz class extends from Foo but it won't define any generic behavior, instead it declares that the generic class used from Foo is String.

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