Java集合总结（二）

来源：互联网发布：dellp2417h的端口编辑：程序博客网时间：2024/05/19 11:19

15.TreeSet对元素的配需方式，让元素自身具备比较性，元素就需要实现Comparable接口，覆盖CompareTo(Object obj)方法。如果元素本身不具备比较方法，则可以定义一个类实现Comparable接口，传递给TreeSet作为参数。示例：

    class HashDemo implements Comparable{        private String name;        private int ID;        public HashDemo(String name, int ID) {            this.name = name;            this.ID = ID;        }        @Override        public int hashCode() {            return this.name.hashCode() + this.ID;        }        @Override        public boolean equals(Object obj) {            if (obj == this)                return true;            if (!(obj instanceof HashDemo))                throw new ClassCastException("类型错误");            HashDemo objDemo = (HashDemo) obj;            return this.name.equals(objDemo.name)                             && this.ID == objDemo.ID;        }        @Override        public String toString() {            return this.name + "\t"                 + ID + "\t"                 + this.getClass().getName();        }        @Override        public int compareTo(Object o) {            HashDemo hd = (HashDemo)o;            if(this.name.compareTo(hd.name)==0)                return this.ID-hd.ID;            else                return this.name.compareTo(hd.name);        }    }    public class Demo {        public static void main(String[] args) {            HashDemo h1                 = new HashDemo("caizhanqi", 2012241001);            HashDemo h2                 = new HashDemo("chenweirong", 2012241002);            HashDemo h3                 = new HashDemo("chenzheng", 2012241003);            HashDemo h4                 = new HashDemo("cuijunbiao", 2012241005);            Set<HashDemo> ts = new TreeSet<HashDemo>();            ts.add(h2);            ts.add(h1);            ts.add(h4);            ts.add(h3);            ts.add(h1);            ts.add(h4);            for(Iterator<HashDemo>                 it = ts.iterator();it.hasNext();){                System.out.println(it.next());            }        }    }

16.示例传递比较方法：

    class MyComparator implements Comparator {        @Override        public int compare(Object o1, Object o2) {            HashDemo hd1 = (HashDemo) o1;            HashDemo hd2 = (HashDemo) o2;            if(hd1.getID()-hd2.getID()==0)                return hd1.getName().compareTo(hd2.getName());            else                return hd1.getID()-hd2.getID();        }    }    public class Demo {        public static void main(String[] args) {            HashDemo h1                 = new HashDemo("caizhanqi", 2012241001);            HashDemo h11                 = new HashDemo("sss", 2012241002);            HashDemo h2                 = new HashDemo("chenweirong", 2012241002);            HashDemo h3                 = new HashDemo("chenzheng", 2012241003);            HashDemo h4                 = new HashDemo("cuijunbiao", 2012241005);            //Set<HashDemo> ts = new TreeSet<HashDemo>();            Set<HashDemo> ts                 = new TreeSet<HashDemo>(new MyComparator());            ts.add(h2);            ts.add(h1);            ts.add(h4);            ts.add(h3);            ts.add(h11);            ts.add(h4);            for (Iterator<HashDemo>                 it = ts.iterator(); it.hasNext();) {                System.out.println(it.next());            }        }    }

17.Map:Key-Value
|–Hashtable:底层是哈希表，不允许null键null值，线程同步，效率低。
|–HashMap:底层是哈希表，允许null键null值，线程不同步，效率高。
|–TreeMap:底层是二叉树，线程不同步，可以用于给Map集合中的key进行排序。
18.Map示例：

    HashDemo h1 = new HashDemo("caizhanqi", 2012241001);    HashDemo h11 = new HashDemo("sss", 2012241002);    HashDemo h2 = new HashDemo("chenweirong", 2012241002);    HashDemo h3 = new HashDemo("chenzheng", 2012241003);    HashDemo h4 = new HashDemo("cuijunbiao", 2012241005);    Map<HashDemo, Integer> map             = new HashMap<HashDemo, Integer>();    // 添加    map.put(h1, 1);    map.put(h2, 2);    map.put(h11, 1);    map.put(h3, 3);    map.put(h4, 4);    show(map);    // 删除    map.remove(h11);    // map.clear();    show(map);    // 判断    System.out.println(map.containsKey(h2));    System.out.println(map.containsValue(22));    // 获取    System.out.println(map.get(h2));    show(map);    System.out.println(map.size());    //迭代输出    Set<HashDemo> keySet = map.keySet();    for(Iterator<HashDemo> it = keySet.iterator();it.hasNext();){        HashDemo key = it.next();        Integer value = map.get(key);        System.out.println(key+"="+value);    }    //另一种输出    Set<Map.Entry<HashDemo, Integer>> mapEntry = map.entrySet();    for (Iterator<Map.Entry<HashDemo, Integer>>         it = mapEntry.iterator(); it.hasNext();) {        Map.Entry<HashDemo, Integer> en = it.next();        HashDemo hd = en.getKey();        Integer num = en.getValue();        System.out.println(hd + "=" + num);    }    //输出所有值    Collection<Integer> values = map.values();    for(Iterator<Integer> it = values.iterator();it.hasNext();)        System.out.println(it.next());

19.输出字符的个数：

    // 输出字符个数    String s = "fjdsnfslmzhvkahvzzzaafspgf";    Map<String, Integer> map = new HashMap<String, Integer>();    for (int i = 0; i < s.length(); i++) {        String c = "" + s.charAt(i);        if (map.containsKey(c)) {            Integer value = map.get(c);            value++;            map.remove(c);            map.put(c, value);            continue;        }        map.put(c, 1);    }    for (it = map.entrySet()            .iterator(); it.hasNext();) {        Map.Entry<String, Integer> entrySet = it.next();        System.out.print(entrySet.getKey()            +"("+entrySet.getValue()+")");    }

20.Collections：集合框架的工具类，排序示例：

    class myComByLength implements Comparator {        @Override        public int compare(Object o1, Object o2) {            String s1 = (String) o1;            String s2 = (String) o2;            if(s1.length()-s2.length()==0)                return s1.compareTo(s2);            else                return s1.length()-s2.length();        }    }    public class newDemo {        public static void main(String[] args) {            List<String> list = new ArrayList<String>();            list.add("1");            list.add("121");            list.add("112");            list.add("113");            list.add("1111");            list.add("132");            list.add("14");            System.out.println(list);            Collections.sort(list);            System.out.println(list);            //Collections.sort(list, new myComByLength());            //System.out.println(list);            System.out.println(Collections.binarySearch(list, "121"));            mySort(list, new myComByLength());            System.out.println(list);            System.out.println(Collections.binarySearch(list, "112", new myComByLength()));            System.out.println("Max="                +Collections.max(list,new myComByLength()));            System.out.println("Min="                +Collections.min(list,new myComByLength()));            System.out.println("Max="                +Collections.max(list,null));            System.out.println("Max="                +Collections.min(list,null));        }        public static <T> void mySort(List<T> list,Comparator<? super T> myComp){            for (int i = 0; i < list.size()-1; i++) {                for (int j = i+1; j < list.size(); j++) {                    if(myComp.compare(list.get(i), list.get(j))>0)                        Collections.swap(list, i, j);                }            }        }    }

21.顺序反转,元素全替换，随机置换元素位置。

    List<String> list = new ArrayList<String>();    list.add("1");    list.add("121");    list.add("112");    list.add("113");    list.add("1111");    list.add("132");    list.add("14");    Collections.sort(list);    System.out.println(list);    Collections.sort(list, Collections.reverseOrder());    System.out.println(list);    Collections.sort(list, new myComByLength());    System.out.println(list);    Collections.sort(list, Collections.reverseOrder(new myComByLength()));    System.out.println(list);    Collections.reverse(list);    System.out.println(list);    Collections.replaceAll(list, "1", "1111111111");    System.out.println(list);    Collections.shuffle(list);    System.out.println(list);

22.线程同步安全的方法：

    class myList extends ArrayList{        private List<String> list;        public List<String> myList(List<String> list) {            return this.list;        }        @Override        public boolean add(Object obj) {            synchronized(this){                return list.add((String) obj);                      }        }        @Override        public boolean remove(Object o) {            synchronized(this){                return list.remove((String)o);                      }        }    }    public class newDemo {        public static void main(String[] args) {            List<String> list = new ArrayList<String>();            list = new myList().myList(list);            Collections.synchronizedList(list);         }    }

23.Arrays:集合框架的工具类，将数组作为集合操作。PS：数组长度是固定的，不能更改，否则会报异常UnsupportedOperationException,而数组转集合，如果数组元素是对象，直接将数组中的元素进行集合存储，如果是基础数据类型，则将数组本身作为元素存储。

    Integer[] arr = {1,2,3,4,5,6};    System.out.println(Arrays.toString(arr));    //将数组转换为集合    List<Integer> list = Arrays.asList(arr);    System.out.println(list);    //基础数据类型数组    int[] arrInt = {1,2,3};    List<int[]> listInt = Arrays.asList(arrInt);    System.out.println(listInt);    System.out.println(listInt.get(0)[2]);    //集合转数组    List<String> listDemo = new ArrayList<String>();    listDemo.add("1");    listDemo.add("1");    listDemo.add("2");    listDemo.add("3");    listDemo.add("4");    listDemo.add("11");    Object[] str1 = listDemo.toArray();    System.out.println(Arrays.toString(str1));    String[] str2 = listDemo.toArray(new String[listDemo.size()]);    System.out.println(Arrays.toString(str2));

0 0