Java 集合框架（List、Set、Map、Iterator、Stack、Properties）

Michael阿明

发布于 2021-09-06 10:06:15

2820

发布于 2021-09-06 10:06:15

文章被收录于专栏：Michael阿明学习之路

文章目录

1. ArrayList

类似动态数组

		ArrayList al = new ArrayList();
        System.out.println("al 的初始大小：" + al.size());
        // al 的初始大小：0
        al.add("C");
        al.add("A");
        al.add("E");
        al.add("B");
        al.add("D");
        al.add("F");

        al.add(1,"A2");
        System.out.println("al size: " + al.size());
        // al size: 7
        System.out.println("al 的内容：" + al);
        // al 的内容：[C, A2, A, E, B, D, F]

        al.remove("F");
        al.remove(2);
        System.out.println("al size: " + al.size());
        // al size: 5
        System.out.println("al 的内容：" + al);
        // al 的内容：[C, A2, E, B, D]

        ArrayList al1 = new ArrayList();
        al1.add(1);
        al1.add(2);
        al1.add(3);
        al1.add(4);
        System.out.println("al1 的内容：" + al1);
        // al1 的内容：[1, 2, 3, 4]
        Object o[] = al1.toArray();
        int sum = 0;
        for(int i = 0; i < o.length; ++i)
            sum += ((Integer)o[i]).intValue();
        System.out.println("sum: " + sum); // sum: 10

2. LinkedList

链表

		LinkedList ll = new LinkedList();
        ll.add("F");
        ll.add("B");
        ll.add("D");
        ll.add("E");
        ll.add("C");
        ll.addLast("Z");
        ll.addFirst("A");
        ll.add(1, 1);
        System.out.println(ll);
        // [A, 1, F, B, D, E, C, Z]
        ll.remove("F");
        ll.remove(2);
        System.out.println(ll);
        // [A, 1, D, E, C, Z]
        ll.removeFirst();
        ll.removeLast();
        System.out.println(ll);
        // [1, D, E, C]
        ll.set(2, "changed");
        System.out.println(ll);
        // [1, D, changed, C]

3. HashSet

哈希集合，无序

		HashSet hs = new HashSet();
        hs.add("A");
        hs.add("B");
        hs.add("C");
        hs.add(1);
        System.out.println(hs);
        // [A, 1, B, C] 无序

4. TreeSet

树set，有序

		TreeSet ts = new TreeSet();
        ts.add("C");
        ts.add("B");
        ts.add("D");
        ts.add("A");
        ts.add("Aa");
        System.out.println(ts);
        // [A, Aa, B, C, D] 有序

5. Iterator、ListIterator

ListIterator 可以修改元素，可以双向遍历，是 Iterator 的扩展

		System.out.println(al);
        // [C, A2, E, B, D]
        Iterator it = al.iterator();
        while (it.hasNext()){
            Object obj = it.next();
            System.out.print(" "+ obj);
        } // 使用 iterator 遍历
        //  C A2 E B D
        System.out.println();

        ListIterator lit = al.listIterator();
        while(lit.hasNext()){
            Object obj = lit.next();
            lit.set(obj+"*");
        }
        System.out.println("打印修改后的内容：");
        it = al.iterator();
        while (it.hasNext()){
            Object obj = it.next();
            System.out.print(" "+ obj);
        } // C* A2* E* B* D*
        System.out.println();

        System.out.println("逆序输出：");
        while(lit.hasPrevious()){
            Object obj = lit.previous();
            System.out.print(" "+ obj);
        } // D* B* E* A2* C*
        System.out.println();

6. HashMap

		// HashMap
        HashMap hm = new HashMap();
        hm.put("Michael", 18);
        hm.put("Ming", 19);

        Set set = hm.entrySet();
        Iterator i = set.iterator();
        while(i.hasNext()){
            Map.Entry me = (Map.Entry) i.next();
            System.out.print(me.getKey() + ":");
            System.out.println(me.getValue());
        }
        int age = ((Integer)hm.get("Michael")).intValue();
        hm.put("Michael", age+2);
        i = set.iterator();
        while(i.hasNext()){
            Map.Entry me = (Map.Entry) i.next();
            System.out.print(me.getKey() + ":");
            System.out.println(me.getValue());
        }

输出：

Ming:19
Michael:18
Ming:19
Michael:20

7. TreeMap

		// TreeMap
        TreeMap tm = new TreeMap();
        tm.put(18, "Michael");
        tm.put(19, "Ming");
        tm.put(0, "Java");
        // values
        Collection col = tm.values();
        Iterator it1 = col.iterator();
        while(it1.hasNext()){
            System.out.println(it1.next());
        }
        // keySet
        Collection col1 = tm.keySet();
        Iterator it2 = col1.iterator();
        while(it2.hasNext()){
            System.out.println(it2.next());
        }
        // entrySet, K V 对
        Collection col2 = tm.entrySet();
        Iterator it3 = col2.iterator();
        while(it3.hasNext()){
            System.out.println(it3.next());
        }

输出：

Java
Michael
Ming
0
18
19
0=Java
18=Michael
19=Ming

8. Stack

Stack 继承于 Vector，Vector 与 ArrayList 类似

class StackDemo{
    static void showpush(Stack st, int a){
        st.push(a);
        System.out.println("入栈：" + a);
        System.out.println(st);
    }
    static void showpop(Stack st){
        Integer a = (Integer) st.pop();
        System.out.println("出栈：" + a);
        System.out.println(st);
    }
    public static void main(String [] args){
        Stack st = new Stack();
        System.out.println(st);
        showpush(st,2);
        showpush(st,4);
        showpush(st,1);
        showpop(st);
        showpop(st);
        showpop(st);
        try{
            showpop(st);//空了，异常
        }
        catch (EmptyStackException e){
            System.out.println("异常：" + e);
        }
    }
}

输出：

[]
入栈：2
[2]
入栈：4
[2, 4]
入栈：1
[2, 4, 1]
出栈：1
[2, 4]
出栈：4
[2]
出栈：2
[]
异常：java.util.EmptyStackException

9. Properties 类

		// Properties : k v 都是字符串的 Hashtable
        Properties capitals = new Properties();
        capitals.put("中国", "北京");
        capitals.put("日本", "东京");
        // capitals.put("美国", "华盛顿");

        Set states = capitals.keySet();
        String country;
        Iterator it4 = states.iterator();
        while(it4.hasNext()){
            country = (String) it4.next();
            System.out.println(country + " : " + capitals.getProperty(country));
        }
        String str = capitals.getProperty("美国", "not found");//若没有key，返回默认值 not found
        System.out.println(str);

输出：

中国 : 北京
日本 : 东京
not found

读写简单数据库

特别适合做简单数据库

class PropertiesFile{
    public static void main(String [] args){
        Properties settings = new Properties();
        try{
            settings.load(new FileInputStream("./count.txt"));
        }
        catch (Exception e){
            settings.setProperty("count", new Integer(0).toString());//没有文件就从0开始计数
        }
        int c = Integer.parseInt(settings.getProperty("count"))+1;
        System.out.println("这是第" + c + "次使用本程序！");
        settings.put("count", new Integer(c).toString());
        try{
            settings.store(new FileOutputStream("./count.txt"), "存储中");
        }
        catch (Exception e){
            System.out.println(e.getMessage());
        }
    }
}

输出：