实例化参数化 class

Question

只是想知道这样做是否正确。我想构造我的参数化 class 的实例，其中一个实例变量是泛型类型。下面的代码有效，但我在主要方法 "SomeObject is a raw type. References to generic type SomeObject should be parameterized".

中收到很多警告

public class SomeObject<T> {

    private String description;

    private T value;


    public SomeObject(String description, T value) {
        this.description = description;
        this.value = value;
    }



public static void main(String args[]){

    List <SomeObject> objectList = new ArrayList<SomeObject>();

    objectList.add(new SomeObject("Object 1: ", true));
    objectList.add(new SomeObject("Object 2: ", 888.00));
    objectList.add(new SomeObject("Object 3: ", "another object"));
    objectList.add(new SomeObject("Object 4: ", '4'));

    for (SomeObject object : objectList){
    System.out.println(object.getDescription() + object.getValue());
    }
}

}

Answer 1

The code below works but I get a lot of warnings in the main method "Object is a raw type. References to generic type Object should be parameterized".

警告是因为您在构造 SomeObject 时没有指定类型参数。即

应该是：

List<SomeObject<?>> objectList = new ArrayList<>();
objectList.add(new SomeObject<Boolean>("Object 1: ", true));
objectList.add(new SomeObject<Double>("Object 2: ", 888.00));
objectList.add(new SomeObject<String>("Object 3: ", "another object"));
objectList.add(new SomeObject<Character>("Object 4: ", '4'));

Answer 2

当你有一个没有类型参数（方括号中的部分）的 SomeObject 时，这称为 raw type，它与使用 [=11= 的擦除相同]. （基本上，擦除意味着它是非通用的。）

您还需要为 List 的 SomeObject 部分提供类型参数。这里我使用了通配符，这意味着列表可以包含任何类型的 SomeObject，但是一旦我们将 SomeObject 放入列表中，我们就不知道它们的原始类型参数是什么了：

List<SomeObject<?>> objectList = new ArrayList<SomeObject<?>>();

objectList.add(new SomeObject<Boolean>("Object 1: ", true));
objectList.add(new SomeObject<Double>("Object 2: ", 888.00));
objectList.add(new SomeObject<String>("Object 3: ", "another object"));
objectList.add(new SomeObject<Character>("Object 4: ", '4'));

for (SomeObject<?> object : objectList) {
    ...;
}

实例化参数化 class

instantiating parameterized class

java

generics

parameterized-constructor