泛型的删除

在类型擦除过程中,Java 编译器将擦除所有类型参数,如果类型参数是有界的,则将每个参数替换为其第一个边界;如果类型参数是无界的,则用Object替换。

考虑以下表示单个链接列表中的节点的通用类:

public class Node<T> {

    private T data;
    private Node<T> next;

    public Node(T data, Node<T> next) {
        this.data = data;
        this.next = next;
    }

    public T getData() { return data; }
    // ...
}

由于类型参数T是无界的,因此 Java 编译器将其替换为Object

public class Node {

    private Object data;
    private Node next;

    public Node(Object data, Node next) {
        this.data = data;
        this.next = next;
    }

    public Object getData() { return data; }
    // ...
}

在以下示例中,通用Node类使用有界类型参数:

public class Node<T extends Comparable<T>> {

    private T data;
    private Node<T> next;

    public Node(T data, Node<T> next) {
        this.data = data;
        this.next = next;
    }

    public T getData() { return data; }
    // ...
}

Java 编译器将绑定类型参数T替换为第一个绑定类Comparable

public class Node {

    private Comparable data;
    private Node next;

    public Node(Comparable data, Node next) {
        this.data = data;
        this.next = next;
    }

    public Comparable getData() { return data; }
    // ...
}