一、Collection

（1）常用方法以ArrayList为例：

public class Hello {
    public static void main(String[] args) {
        List list = new ArrayList();
        //add():添加单个元素
        list.add("你好");
        list.add(10);
        list.add(true);
        //remove():删除指定元素
//        list.remove(0);//删除第一个元素
//        list.remove(true);//删除某个元素
        //contains():判断一个元素是否存在
        boolean contains = list.contains(10);
        System.out.println(contains);
        //size():获取一个元素的个数
        System.out.println(list.size());
        //isEmpty():判断一个元素是否为空
        System.out.println(list.isEmpty());
        //clear():清空
        list.clear();
        //addAll():添加多个继承Collection元素
        list.addAll(list);
        //containsAll():判断多个元素是否存在
        System.out.println(list.containsAll(list));
        //removeAll():删除多个元素
        list.removeAll(list);
        System.out.println(list);
    }
}

（2）iterator迭代器遍历：

public class Hello {
    public static void main(String[] args) {
        Collection cl = new ArrayList();
        cl.add(new Book("三国演义","罗贯中"));
        cl.add(new Book("雄安里飞到","韩顺平"));
        cl.add(new Book("蛤蟆非全","里蛤蟆"));

        Iterator iterator = cl.iterator();
        //ctrl+j生成方法快捷键   itit生成Interator迭代器
        while (iterator.hasNext()){
            Object obj = iterator.next();
            System.out.println(obj);
        }
        //这个时候指针已经到最后面了需要重置指针,就可以重新遍历了
        iterator = cl.iterator();
    }
}

class Book{
    private String name;
    private String author;

    public Book(String name, String author) {
        this.name = name;
        this.author = author;
    }

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + ''' +
                ", author='" + author + ''' +
                '}';
    }
}

（3）使用增强for循环：

public class Hello {
    public static void main(String[] args) {
        Collection cl = new ArrayList();
        cl.add(new Book("三国演义", "罗贯中"));
        cl.add(new Book("雄安里飞到", "韩顺平"));
        cl.add(new Book("蛤蟆非全", "里蛤蟆"));
        //可以用在数组，也可以用在集合 快捷键 I
        for (Object obj : cl) {
            System.out.println(obj);
        }
    }
}

class Book {
    private String name;
    private String author;

    public Book(String name, String author) {
        this.name = name;
        this.author = author;
    }

    @Override
    public String toString() {
        return "Book{" +
                "name='" + name + ''' +
                ", author='" + author + ''' +
                '}';
    }
}

案例：创建3个Dog对象name,age放到ArrayList中。使用for增强和迭代器循环

public class Hello {
    public static void main(String[] args) {
        Collection cl = new ArrayList();
        cl.add(new Dog("小黑", 1));
        cl.add(new Dog("小黄", 2));
        cl.add(new Dog("小白", 3));
        //使用增强for循环遍历
        for (Object obj : cl) {
            System.out.println(obj);
        }
        System.out.println("");
        //使用迭代器遍历
        Iterator iterator = cl.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }
    }
}

class Dog {
    private String name;
    private int age;

    public Dog(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "name='" + name + ", age=" + age;
    }
}

二、List

实现的集合有：ArrayList、 Vector、LinkedList  可重复添加、有序

（1）ArrayList：

public class Hello {
    public static void main(String[] args) {
        //1.List集合类中元素有序(即添加顺序和取出顺序一致)、且可重复
        List list = new ArrayList();
        //插入一个值第一个值可以为索引
        list.add("jack");
        list.add(1,"贾宝玉");
        list.addAll(list);//一次加入一个数组
        System.out.println(list.indexOf("jack"));//返回字符第一次出现的位置
        System.out.println(list.lastIndexOf("jack"));//返回字符最后一次出现的位置
        list.remove(0);//删除索引的元素
        list.set(1,"marry");//设置索引为1的值为marry。一定要存在
        list.subList(0,2);//返回0-2的集合0<=x<2 前闭后开
        System.out.println("list="+list);
        //2.List集合中的每个元素都有对其对应的顺序索引，即支持索引
        //  索引是从0开始
        System.out.println(list.get(3)); //获取元素
    }
}

案例：添加10个以上的元素，在2号位插入一个元素，韩顺平教育，获得第5个元素，删除第6元素，修改第7个元素，使用迭代器遍历,ArrayList

public class Hello {
    public static void main(String[] args) {
        List ls = new ArrayList();
        ls.add("hello1");
        ls.add("hello2");
        ls.add("hello3");
        ls.add("hello4");
        ls.add("hello5");
        ls.addAll(ls);
        ls.add(1,"韩顺平教育");
        System.out.println(ls);
        System.out.println(ls.get(4));
        ls.remove(5);
        ls.set(6,"你好");
        System.out.println(ls);
    }
}

案例：新建Book对象Arraylist存储，冒泡排序，遍历

public class Hello {
    public static void main(String[] args) {
        ArrayList al = new ArrayList();
        al.add(new Book("红楼梦","曹雪芹",100));
        al.add(new Book("水浒传","施耐庵",80));
        al.add(new Book("西游记","吴承恩",90));
        for (int i = 0; i < al.size(); i++) {
            for (int j = 0; j < al.size()-i-1; j++) {
                Book book1 =(Book) al.get(j);
                Book book2 =(Book) al.get(j+1);
                if (book1.getPrice()>book2.getPrice()){
                    al.set(j,book2);
                    al.set(j+1,book1);
                }
            }
        }
        for (Object o :al) {
            System.out.println(o);
        }
    }
}

class Book {
    private String name;
    private String author;
    private double price;

    public Book(String name, String author, double price) {
        this.name = name;
        this.author = author;
        this.price = price;
    }

    public double getPrice() {
        return price;
    }

    @Override
    public String toString() {
        return name + "tt" + author + "tt" + price;
    }
}

（2）Vector：

• 底层也是一个对象
• Vector线程安全，线程同步
• 开发中需要线程安全就使用Vector
• 方法同ArrayList方法一样

public class Hello {
    public static void main(String[] args) {
        Vector vector = new Vector();
        for (int i = 0; i < 10; i++) {
            vector.add(i);
        }
        System.out.println(vector);
    }
}

（3）LinkedList

• LinkedList底层实现了双向列表和双向列表特点
• 可以添加任意元素(元素可以重复)，包括null
• 线程不安全，没有实现同步

1.双向链表的底层原理

public class Hello {
    public static void main(String[] args) {
        //模拟一个简单的双向列表
        Node jack = new Node("jack");
        Node tom = new Node("tom");
        Node hsp = new Node("韩顺平");
        //连接三个节点，形成双链表
        //jack->tom->hsp
        jack.next = tom;
        tom.next = hsp;
        //hsp->tom->jack
        tom.pre=jack;
        hsp.pre = tom;

        Node first = jack;//让first引用指向jack，就是双向链表的头
        Node last = hsp; //让last引用指向jack，就是双向链表的尾

        System.out.println("演示从头到尾遍历");
        while (true){
            if (first == null){
                break;
            }
            System.out.println(first);
            first = first.next;
        }

        //演示插入一个节点 smith
        Node smith = new Node("smith");
        smith.pre = jack;
        smith.next = tom;
        jack.next = smith;
        tom.pre = smith;

        System.out.println("演示从尾到头遍历");
        while (true){
            if (last == null){
                break;
            }
            System.out.println(last);
            last = last.pre;
        }
    }
}

//定义一个Node类，Node 对象 的表示双向列表的一个节点
class Node{
    public Object item; //真正存放数据
    public Node next; //下一个
    public Node pre;  //上一个

    public Node(Object name) {
        this.item = name;
    }

    @Override
    public String toString() {
        return "Node name" + item;
    }
}

2.linkedList的演示

public class Hello {
    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        list.add(1);
        list.add(1);
        list.remove(0);
        list.set(0,"hsp");
        System.out.println(list.get(0));
    }
}

（4）ArrayList与LinkedList的选取：

• 如果我们改查的操作多，选择ArrayList
• 如果我们增删的操作多，选择LinkeList
• 一般来说，在项目中，80%~90%都是查询因此大部分情况下回选择ArrayList
• 在一个项目中，根据业务灵活选择，也可能这样，一个模块使用的是ArrayList，另外一个模块是LinkedList

三、Set

定义：无序(添加和取出的顺序不一致)，没有索引，不允许重复元素，所以最多包含一个null，实现的类有TreeSet、HashSet、LinkedHashSet

常用方法和Collection一样因为也是继承与他。

（1）Set接口方法：

public class Hello {
    public static void main(String[] args) {
        //1.以Set 接口的实现类 HashSet 来讲解Set接口方法
        Set set = new HashSet();  //没有get方法，不能使用for循环索引来获取
        set.add("john"); //添加
        set.add("lucy");
        set.add("john");
        set.add("mary");//无序：添加顺序，与取出的顺序不同,取出的顺序是一样的，而且不能重复
        System.out.println(set); //[mary, john, lucy]
        //遍历 使用迭代器
        Iterator iterator = set.iterator();
        while (iterator.hasNext()) {
            Object next =iterator.next();
            System.out.println(next);
        }
        for (Object o :set) {
            System.out.println(o);
        }

    }
}

（2）HashSet：

数据不能重复，取出与存入的顺序不同，是否重复比较的是地址值

案例：定义一个Employee类，private属性name,age要求创建3个Employee放入HashSet中，名字和年龄相同时表示重复

public class Hello {
    public static void main(String[] args) {
        Set set = new HashSet();
        set.add(new Employee("张三",14));
        set.add(new Employee("张三",14));
        set.add(new Employee("张三",15));
        System.out.println(set);
    }
}

class Employee{
    private String name;
    private int age;

    public Employee(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return age == employee.age && Objects.equals(name, employee.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + ''' +
                ", age=" + age +
                '}';
    }
}

案例2：定义一个Employee类，该类包含:private成员属性name,sal,birthday(MyDate类·型)，其中 birthday 为 MyDate类型(属性包括:year, month, day),要求:1.创建3个Employee放入 HashSet中2.当name和birthday的值相同时，认为是相同员工，不能添加到HashSet集合中

public class Hello {
    public static void main(String[] args) {
        Set set = new HashSet();
        set.add(new Employee("张三",14,new MyDate(1,1,1)));
        set.add(new Employee("张三",14,new MyDate(1,1,1)));
        set.add(new Employee("张三",15,new MyDate(1,1,1)));
        System.out.println(set);
    }
}

class Employee{
    private String name;
    private int age;
    private MyDate date;

    public Employee(String name, int age, MyDate date) {
        this.name = name;
        this.age = age;
        this.date = date;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Employee employee = (Employee) o;
        return age == employee.age && Objects.equals(name, employee.name) && Objects.equals(date, employee.date);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age, date);
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + ''' +
                ", age=" + age +
                ", date=" + date +
                '}';
    }
}

class MyDate{
    private int year;
    private int month;
    private int day;

    public MyDate(int year, int month, int day) {
        this.year = year;
        this.month = month;
        this.day = day;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        MyDate myDate = (MyDate) o;
        return year == myDate.year && month == myDate.month && day == myDate.day;
    }

    @Override
    public int hashCode() {
        return Objects.hash(year, month, day);
    }
}

（3）LinkedHashSet:

定义：是HashSet的子类，所以方法也是一样的，但是啊是按顺序添加与取出

案例：Car类(name:price),如果name和price一样则认为是相同，就不能添加

public class Hello {
    public static void main(String[] args) {
        LinkedHashSet linkedHashSet = new LinkedHashSet();
        linkedHashSet.add(new Car("马自达",15));
        linkedHashSet.add(new Car("马自达",15));
        linkedHashSet.add(new Car("宝马",19));
        System.out.println(linkedHashSet);
    }
}
class Car{
    private String name;
    private double price;

    public Car(String name, double price) {
        this.name = name;
        this.price = price;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof Car)) return false;
        Car car = (Car) o;
        return Double.compare(car.price, price) == 0 && Objects.equals(name, car.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, price);
    }

    @Override
    public String toString() {
        return "Car{" +
                "name='" + name + ''' +
                ", price=" + price +
                '}';
    }
}

四、Map

（1）map的常用方法：

public class Hello {
    public static void main(String[] args) {
        Map map = new HashMap();
        map.put("邓超","孙俪");
        map.put("王宝强","马蓉");
        map.put("宋喆","马蓉");
        map.put("hsp","韩顺平");
        map.put(null,"空");
        map.put("空",null); //添加
        map.remove(null);//删除
        System.out.println(map.get("空"));
        System.out.println(map.size()); //返回有几对
//        map.clear();//清空
        System.out.println(map.isEmpty()); //判断map是否为空
        System.out.println(map.containsKey("hsp")); //判断某个是否存在
        System.out.println(map);
    }
}

（2）map的循环： keySet 、map.values() 、entryMap

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        Map map = new HashMap();
        map.put("邓超","孙俪");
        map.put("王宝强","马蓉");
        map.put("宋喆","马蓉");
        map.put("hsp","韩顺平");
        map.put(null,"空");
        map.put("空",null);
        //map接口的遍历
        //第一组取出所有的key
        Set keySet = map.keySet();
        //增强for循环,迭代器，
        for (Object key :keySet) {
            System.out.println(keySet+"====="+map.get(key));
        }
        //第二组取出所有value
        Collection values = map.values();
        //增强for，迭代器
        System.out.println("----取出所有Value-----");
        for (Object val :values) {
            System.out.println(val);
        }
        //第三组：通过entrySet获取key-value
        Set entrySet = map.entrySet(); //EntrySet<Map.Entry<K,V>>
        //增强for,迭代器
        for (Object entry : entrySet) {
            //将entry转成mapEntry
            Map.Entry m = (Map.Entry) entry;
            System.out.println(m.getKey()+"====="+m.getValue());
        }
    }
}

（3）hashMap：

public class Hello {
    public static void main(String[] args) {
        Map map = new HashMap();
        Employee a1 = new Employee("张三", 20000, 1);
        Employee a2 = new Employee("王五", 19000, 2);
        Employee a3 = new Employee("李四", 10000, 3);
        map.put(a1.getId(), a1);
        map.put(a2.getId(), a2);
        map.put(a3.getId(), a3);
        Set keySet = map.keySet();
        for (Object key : keySet) {
            Employee employee = (Employee) map.get(key);
            if (employee.getSalary() > 18000) System.out.println(key + "======" + employee);
        }
    }
}

class Employee {
    private String name;
    private double salary;
    private int id;

    public Employee(String name, double salary, int id) {
        this.name = name;
        this.salary = salary;
        this.id = id;
    }

    public int getId() {
        return id;
    }

    public double getSalary() {
        return salary;
    }

    @Override
    public String toString() {
        return "Employee{" +
                "name='" + name + ''' +
                ", salary=" + salary +
                ", id=" + id +
                '}';
    }
}

（4）Hashtable:不允许空值null

public class Hello {
    public static void main(String[] args) {
        Hashtable hashtable = new Hashtable();
        hashtable.put("john", 100);
//        hashtable.put(null, 100); //报错
//        hashtable.put(100, null); //报错
        System.out.println(hashtable);
    }
}

（5）Properties：一般用读取配置文件

继承了HashTable所有键和值不能为空，后面会说读取properties文件很重要

public class Hello {
    public static void main(String[] args) {
        Properties properties = new Properties();
        properties.put("123",123);
        properties.put("三","四");
        properties.remove("123");
        properties.setProperty("三","五");
        System.out.println(properties.get("三"));
    }
}

（6）技术选型：

四、TreeSet

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        /*
        * 当我们使用无参构造器，创建TreeSet时，任是无序的
        * 当我们希望添加元素，按照字符串大小排序
        * 使用treeSet，提供的构造器，可以传入一个比较值
        * */
        TreeSet treeSet = new TreeSet(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                return ((String) o2 ).compareTo((String) o1);
            }
        });
        treeSet.add("jack");
        treeSet.add("tom");
        treeSet.add("a");
        treeSet.add("sp");
        System.out.println(treeSet);
    }
}

五、TreeMap

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        //无参构造器，没有排序按字母排序
        //有参传个比较器
        TreeMap map = new TreeMap(new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                //按字符的降序
//                return ((String) o2).compareTo((String) o1);
                return ((String) o2).length() - ((String) o1).length(); //打印一个
            }
        });
        map.put("a","A");
        map.put("b","B");
        map.put("c","C");
        map.put("d","D");
        System.out.println(map);
    }
}

六、Collections工具类

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        List list = new ArrayList();
        list.add("tom");
        list.add("jack");
        list.add("smith");
        list.add("marry");
        //reserve(list) 反转List中元素的顺序
        Collections.reverse(list);
        System.out.println(list);
        //shuffle(list) 对数组进行随机排序
        Collections.shuffle(list);
        System.out.println(list);
        //sort(list) 对元素进行升序 自然排序 abcdefg
        Collections.sort(list);
        System.out.println(list);
        //需要自己定义排序 sort(lis,comparaor)
        Collections.sort(list, new Comparator() { //按字符串长度排序
            @Override
            public int compare(Object o1, Object o2) {
                return ((String) o1).length() - ((String) o2).length();
            }
        });
        System.out.println(list);
        //swap(lis,i,j) 将list的指定元素 i j 处元素进行交换
        Collections.swap(list,1,2);
        System.out.println(list);
        //返回自然排序list中最大值
        System.out.println(Collections.max(list));
        //根据自定义的比较返沪最大的
        Object o = Collections.max(list, new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                return ((String) o1).length() - ((String) o2).length();
            }
        });
        System.out.println(o);
        //查抄集合中指定元素出现的次数
        System.out.println(Collections.frequency(list,"tom"));
        //copy复制list
    }
}

七、作业

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        News news1 = new News("新冠确诊病例超千万，数百万印度教信徒赴恒河“圣浴”引民众担忧");
        News news2 = new News("男子突然想起2个月前钓的鱼还在网兜里，捞起一看赶紧放生");
        List list = new ArrayList();
        list.add(news1);
        list.add(news2);
        Collections.sort(list, new Comparator() {
            @Override
            public int compare(Object o1, Object o2) {
                return ((News) o2).getTitle().compareTo(((News) o1).getTitle());
            }
        });
        for (Object news : list) {
            System.out.println(news.toString().substring(0,15)+"...");
        }
    }
}

class News {
    private String title;

    public News(String title) {
        this.title = title;
    }

    public String getTitle() {
        return title;
    }

    @Override
    public String toString() {
        return title;
    }
}

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        ArrayList arrayList = new ArrayList();
        arrayList.add("123"); //添加一个元素
        arrayList.remove("123");// 移除某个元素
        System.out.println(arrayList.contains("123")); //判断某个元素是否存在
        System.out.println(arrayList.size()); //获取元素大小
        System.out.println(arrayList.isEmpty());//判断元素是否为空
        arrayList.clear();//清空
        ArrayList arrayList1 = new ArrayList();
        arrayList1.add(new Car("宝马",190000));
        arrayList1.add(new Car("宾利",500000));
        arrayList.addAll(arrayList1);//i俺家多个元素
        System.out.println(arrayList.containsAll(arrayList1));//判断多个元素是否存在
        arrayList1.removeAll(arrayList);//移除多个元素
        for (Object car : arrayList) {
            System.out.println(car);
        }
    }
}

class Car{
    private String name;
    private double price;

    public Car(String name, double price) {
        this.name = name;
        this.price = price;
    }

    @Override
    public String toString() {
        return "Car{" +
                "name='" + name + ''' +
                ", price=" + price +
                '}';
    }
}

@SuppressWarnings({"all"}) //取消文件警告
public class Hello {
    public static void main(String[] args) {
        Map map = new HashMap();
        map.put("jack", 650);
        map.put("tom", 1200);
        map.put("smith", 2900);
        System.out.println("初始化后工资: " + map);
        map.put("jack", 2600);
        System.out.println("jack更新之后工资: " + map);
        Set keySet = map.keySet();
        for (Object o : keySet) {
            map.put(o, (int) map.get(o) + 100);
        }
        System.out.println("所有员工加一百："+map);
        Set entrySet = map.entrySet();
        for (Object set : entrySet) {
            Map.Entry entry = (Map.Entry) set;
            System.out.println(entry.getKey()+"=====>"+entry.getValue());
        }
    }
}

最后

以上就是彩色小笼包为你收集整理的第十三章：集合 一、Collection二、List三、Set四、Map四、TreeSet五、TreeMap六、Collections工具类七、作业的全部内容，希望文章能够帮你解决第十三章：集合 一、Collection二、List三、Set四、Map四、TreeSet五、TreeMap六、Collections工具类七、作业所遇到的程序开发问题。

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