Question

package test_run;

import java.util.ArrayList;
import java.util.Iterator;

class Al_class
{
  int x;

  Al_class() {
    x=0;
  }

  void increment(){
      ++x;
  }

  int get_value(){
      return x;
  }

    ArrayList<Al_class> class_declare(){
    //void class_declare(){
      Al_class alc1 = new Al_class();
      Al_class alc2 = new Al_class();
      Al_class alc3 = new Al_class();
      alc1.increment();
      alc1.increment();
      alc1.increment();
      alc2.increment();

      ArrayList al = new ArrayList();
      al.add(alc1);
      al.add(alc2);
      al.add(alc3);
      return al;
  }



} ///:~

class Main
{

  public static void main(String[] args) {
    Al_class a = new Al_class();
    ArrayList<Al_class> b;

    b=a.class_declare();
    a.class_declare();
    System.out.print(" Arraylist size= "+ b.size());

    for (Al_class c : b ){

        System.out.print("\n" + c.get_value() + "\n");
    }
    b.remove(0);
    System.out.print(" Arraylist size= "+ b.size());

    Iterator it= b.iterator();
    while (it.hasNext()) {
        System.out.print("\n" + it.next());
        // Al_class e=it.next();
        // System.out.print("\n" + e.get_value());          
    }
  }
}

如何使用迭代器调用对象函数get_value？它不是作业，而是自学。

Answer 1

您必须使用泛型，这意味着将Iterator更改为Iterator<A1_class>：

Iterator<A1_class> it= b.iterator();
while (it.hasNext()) {
    Al_class e=it.next();
    System.out.print("\n" + e);
    System.out.print("\n" + e.get_value());          
}

Answer 2

你可以通过几种方式

明确投射

while (it.hasNext()) {
    Object o = it.next();
    if(o instanceof Al_class){
        Al_class e=(Al_class)o;
        System.out.print("\n" + e.get_value());  
    } 
}

<强>泛型

Iterator<A1_class> it= b.iterator();
while (it.hasNext()) {
    Al_class e=it.next();
    System.out.print("\n" + e.get_value());          
}

你真的不应该再进行明确的类型检查了，但是它仍然存在并且用例有限。

Iterator在java中调用类函数

2 个答案: