javaSE21/9/17

集合

List

List接口的使用

public class Test {
    public static void main(String[] args){
        //添加数字类型的数据
        List list = new ArrayList();
        //在集合中添加数据时会自动装箱
        list.add(20);//该数据已经变成引用类型
        list.add(30);
        list.add(40);
        list.add(50);
        list.add(60);

        System.out.println(list.size());
        System.out.println(list.toString());
        //删除
        list.remove(0);//删除角标0的元素
        list.remove(new Integer(40));//将数据强转也能删除数据
        System.out.println(list.toString());
        //subList方法,子集合
        List subList = list.subList(0,2);//含头不含尾
        System.out.println(subList.toString());

    }
}

List实现类

ArrayList

• 用数组的结构实现，查询快，增删慢
• 运行速率快，线程不安全
• 源码分析
  默认容量大小DEFAULT_CAPACITY = 10；
  存放元素的数组elementData

public class Test {
    public static void main(String[] args){
        ArrayList arrayList = new ArrayList();//实例化一个集合
        //添加
        Student s1 = new Student("张三",20);
        Student s2 = new Student("李四",18);
        Student s3 = new Student("王五",19);
        Student s4 = new Student("赵六",22);
        Student s5 = new Student("小明",20);
        arrayList.add(s1);
        arrayList.add(s2);
        arrayList.add(s3);
        arrayList.add(s4);
        arrayList.add(s5);
        System.out.println("-----------添加-------------");
        System.out.println(arrayList.size());
        System.out.println(arrayList.toString());
        //删除
        arrayList.remove(1);
        System.out.println("-----------删除-------------");
        System.out.println(arrayList.size());
        System.out.println(arrayList.toString());
        //遍历
        Iterator it = arrayList.iterator();
        System.out.println("-----------Iterator遍历-------------");
        while ((it.hasNext())){
            Student s =(Student) it.next();
            System.out.println(s.toString());
        }
        //ListIterator可从前往后，也可从后往前遍历
        ListIterator lit = arrayList.listIterator();
        //从前往后遍历
        System.out.println("-----------ListIterator前-------------");
        while ((lit.hasNext())){
            Student st =(Student) lit.next();
            System.out.println(st.toString());
        }
        //从后往前遍历
        System.out.println("-----------ListIterator后-------------");
        while (lit.hasPrevious()){
            Student stu = (Student) lit.previous();
            System.out.println(stu.toString());
        }
        //判断
        System.out.println(arrayList.contains(s1));
    }
}

Vector

• 用数组的结构实现，查询快，增删慢
• 运行速率慢，线程安全

public class Test {
    public static void main(String[] args){
        Vector vector = new Vector();
        //添加
        vector.add("草莓");
        vector.add("葡萄");
        vector.add("桔子");
        System.out.println(vector.size());
        System.out.println(vector.toString());
        //遍历 使用枚举器
        Enumeration enu = vector.elements();
        while (enu.hasMoreElements()){
            String str = (String) enu.nextElement();
            System.out.println(str);
        }
    }
}

LinkedList

• 用链表结构实现，增删快，查询慢
• 双向链表

public class Test {
    public static void main(String[] args){
        //创建集合
        LinkedList linkedList = new LinkedList();
        //添加
        Student s1 = new Student("张三",20);
        Student s2 = new Student("李四",18);
        Student s3 = new Student("王五",19);
        linkedList.add(s1);
        linkedList.add(s2);
        linkedList.add(s3);
        System.out.println(linkedList.size());
        System.out.println(linkedList.toString());
        //获取
        System.out.println(linkedList.indexOf(s1));//获取某个数据的位置

    }
}