Java Generics 简明教程
Java Generics - No Instance
不能在方法内部使用类型参数实例化其对象。
public static <T> void add(Box<T> box) {
//compiler error
//Cannot instantiate the type T
//T item = new T();
//box.add(item);
}
如需实现这种功能,请使用反射。
public static <T> void add(Box<T> box, Class<T> clazz)
throws InstantiationException, IllegalAccessException{
T item = clazz.newInstance(); // OK
box.add(item);
System.out.println("Item added.");
}
Example
package com.tutorialspoint;
public class GenericsTester {
public static void main(String[] args)
throws InstantiationException, IllegalAccessException {
Box<String> stringBox = new Box<String>();
add(stringBox, String.class);
}
public static <T> void add(Box<T> box) {
//compiler error
//Cannot instantiate the type T
//T item = new T();
//box.add(item);
}
public static <T> void add(Box<T> box, Class<T> clazz)
throws InstantiationException, IllegalAccessException{
T item = clazz.newInstance(); // OK
box.add(item);
System.out.println("Item added.");
}
}
class Box<T> {
private T t;
public void add(T t) {
this.t = t;
}
public T get() {
return t;
}
}
这会产生以下结果 −
Item added.