java有界类型参数的实例用法

public class Box<T> {
 
    private T t;          
 
    public void set(T t) {
        this.t = t;
    }
 
    public T get() {
        return t;
    }
 
    public <U extends Number> void inspect(U u){
        System.out.println("T: " + t.getClass().getName());
        System.out.println("U: " + u.getClass().getName());
    }
 
    public static void main(String[] args) {
        Box<Integer> integerBox = new Box<Integer>();
        integerBox.set(new Integer(10));
        integerBox.inspect("some text"); // error: this is still String!
    }
}

Box.java:21: <U>inspect(U) in Box<java.lang.Integer> cannot
  be applied to (java.lang.String)
                        integerBox.inspect("10");
                                  ^
1 error

public class NaturalNumber<T extends Integer> {
 
  private T n;
 
  public NaturalNumber(T n)  { this.n = n; }
 
  public boolean isEven() {
    return **n.intValue()** % 2 == 0;
  }
 
  // ...
}

public class Box<T> {

    private T obj;

    public Box() {}

    public T getObj() {
        return obj;
    }

    public void setObj(T obj) {
        this.obj = obj;
    }

    public Box(T obj) {
        super();
        this.obj = obj;
    }

    public <Q extends Number> void inspect(Q q) {
        System.out.println(obj.getClass().getName());
        System.out.println(q.getClass().getName());
    }
}

 Box<String> b = new Box<>();
 b.setObj("Hello");
 b.inspect(12);
 b.inspect(1.5);
 // b.inspect(true); // 编译出错