package com.heima.collection;
import java.util.ArrayList;
import java.util.Collection;
import com.heima.bean.Student;
@SuppressWarnings({ "rawtypes", "unchecked" })
public class Demo3_Collection {
/**
* * A:集合的遍历
* 其实就是依次获取集合中的每一个元素。
* B:案例演示
* 把集合转成数组,可以实现集合的遍历
* toArray()
*/
public static void main(String[] args) {
//demo1();
Collection c = new ArrayList();
问题? c.add(new Student("张三", 23)); //Object obj = new Student("张三",23);
c.add(new Student("李四", 24));
c.add(new Student("王五", 25));
c.add(new Student("赵六", 26));
Object[] arr = c.toArray(); //将集合转换成数组
for (int i = 0; i < arr.length; i++) {
//System.out.println(arr[i]);
Student s = (Student)arr[i]; //向下转型
System.out.println(s.getName() + "..." + s.getAge());
}
}
public static void demo1() {
Collection c = new ArrayList();
c.add("a");
c.add("b");
c.add("c");
c.add("d");
Object[] arr = c.toArray(); //将集合转换成数组
for(int i = 0; i < arr.length; i++) {
System.out.println(arr[i]);
}
}
}
问题出处在上面代码已经标出: 请问为什么在 c.add(new Student("张三", 23)); //Object obj = new Student("张三",23); 中, new Student("张三",23)会自动提升为Object类??? |
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