JavaSE之简单集合的使用

/**
* Collection体系集合
* 1）List集合：有下标，元素可重复
* ArrayList: 数据结构实现，查询快，增删慢（运行效率快，线程不安全）
* Vector: 数据结构实现，查询快，增删慢（运行效率慢，线程安全）
* LinkedList: 链表结构实现，增删快，查询慢
* 2）Set集合：无下标，元素不可重复
* HashSet: 基于hashcode实现元素不重复；当元素的哈希码相等时，会调用==或equals确认，相等则拒绝存入
* LinledHashSet: 链表实现HashSet,按照链表存储，可保留元素的插入顺序
* TreeSet: 可以排序, 但是需要指定排序的算法
*
* 泛型：泛型类、泛型接口、泛型方法
* <T>泛型：类型占位符，表示一种引用类型
* 泛型优点：提高代码重用性、防止类型转换异常，提高代码的安全性
*/

 

class StudentTest {
    //实体类
    private String name;
    private int    age;
    //无参构造
    public StudentTest() {}
    //有参构造
    public StudentTest(String name,int age) {
        this.name = name;
        this.age = age;
    }
    // set/get方法
    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
    //toString（作用）：返回一个字符串，将该Java对象的内存地址经过哈希算法得出int类型的值；再将其转换成十六进制。
    @Override
    public String toString() {
        return "Student [name=" + name + ", age=" + age + "]";
    }
}

 

/**
* 1、ArrayList的简单使用
*/

public class GatherTest {
    public static void main(String[] args) {
        //使用集合Collection保存StudentTest对象
        Collection<StudentTest> coll = new ArrayList<>();
        coll.add(new StudentTest("zs",20));
        coll.add(new StudentTest("ls",22));
        coll.add(new StudentTest("ww",16));

        System.out.println("==========使用迭代器进行遍历输出==========>");
        Iterator<StudentTest> it = coll.iterator();
        while (it.hasNext()) {
            System.out.println(it.next());
        }

        System.out.println("==========使用增强for循环进行遍历输出==========>");
        for (StudentTest student : coll) {
            System.out.println(student);
        }

        System.out.println("---------------清除所有对象--------------");
        coll.clear();
        System.out.println(coll);

        System.out.println("---------------判断是否为空--------------");
        System.out.println(coll.isEmpty());
    }
}

 

/**
* 2、ArrayList的简单使用
*/

class ArrayTest {
    public static void main(String[] args) {
        List<StudentTest> list = new ArrayList<>();
        list.add(new StudentTest("zs",20));
        list.add(new StudentTest("ls",22));
        Iterator<StudentTest> iterat = list.iterator();
        while (iterat.hasNext()) {
            System.out.println(iterat.next());
        }
        System.out.println("---------添加、以下标添加----------");
        list.add(1,new StudentTest("zw",19));
        Iterator<StudentTest> iterat1 = list.iterator();
        while (iterat1.hasNext()) {
            System.out.println(iterat1.next());
        }
        System.out.println("---------下标获取对象并输出----------");
        System.out.println(list.get(1));

        System.out.println("---------以下标删除----------");
        list.remove(2);
        Iterator<StudentTest> iterat2 = list.iterator();
        while (iterat2.hasNext()) {
            System.out.println(iterat2.next());
        }
        System.out.println("---------以下标修改值----------");
        list.set(1, new StudentTest("ls",22));
        Iterator<StudentTest> iterat3 = list.iterator();
        while (iterat3.hasNext()) {
            System.out.println(iterat3.next());
        }

    }
}

 

/**
* 3、LinkedList的简单使用
*/

class Gather {
    public static void main(String[] args) {
        LinkedList<StudentTest> at = new LinkedList<>();
        at.add(new StudentTest("zs",20));
        System.out.println("---------添加、以下标添加----------");
        at.addLast(new StudentTest("ls",22));
        at.add(1,new StudentTest("ww",18));
        Iterator<StudentTest> it = at.iterator();
        while(it.hasNext()) {
            StudentTest st = it.next();
            System.out.println(st.getName()+"--->"+st.getAge());
        }
        System.out.println("---------下标获取对象并输出----------");
        System.out.println(at.get(1));

        System.out.println("---------以下标删除----------");
        at.remove(1);
        Iterator<StudentTest> iterat2 = at.iterator();
        while (iterat2.hasNext()) {
            System.out.println(iterat2.next());
        }
        System.out.println("---------以下标修改值----------");
        at.set(1, new StudentTest("wz",17));
        Iterator<StudentTest> iterat3 = at.iterator();
        while (iterat3.hasNext()) {
            System.out.println(iterat3.next());
        }
    }
}

 

//4、案例: 集合存储字符串元素,例如: "ldh","guodegang","lyf","gyy","liuyifei"
//找出集合中字符串长度为3的元素;
// 找出集合中字符串长度大于5的元素；

class ListTest {
        public static void main(String[] args) {
            //将字符串元素用数组存储
            String[] as = {"ldh","guodegang","lyf","gyy","liuyifei"};
            //将数组转换为List集合
            List<String> list = Arrays.asList(as);
            List<String> list2 = new ArrayList<String>();
            List<String> list3 = new ArrayList<String>();
            //用循环遍历判断
            for(String a: list) {
                if(a.length()==3){
                    list2.add(a);
                }else if(a.length()>5) {
                    list3.add(a);
                }
            }
            System.out.println("长度为3的元素："+list2+"\n"+"长度大于5的元素："+list3);
        }
}