学习java之HashMap和TreeMap

妖狐艹你老母 2021-12-13 21:49 311阅读 0赞

HashMap和TreeMap是Map接口的两种实现，ArrayDeque和LinkedList是Queue接口的两种实现方式。下面的代码是我今天学习这四个数据结构之后写的。还是不熟悉，TreeMap中的其余构造方法我还没有实现，真搞不懂同样的数据结构用java却写的这么麻烦。。

package regexp;
    
    import java.util.Collection;
    import java.util.Comparator;
    import java.util.HashMap;
    import java.util.Iterator;
    import java.util.LinkedList;
    import java.util.Map;
    import java.util.NoSuchElementException;
    import java.util.Queue;
    import java.util.Set;
    import java.util.TreeMap;
    
    public class test {
        public static void main(String args[]) throws NoSuchElementException{
            //Queue接口的实现
            Queue<Integer> q = new LinkedList<Integer>();    //通过LinkedList实现Queue接口
    //        Queue<Integer> q = new ArrayDeque<Integer>();    //通过LinkedList实现Queue接口
            for(int i=0;i<10;i++) {
                q.add(i+1);
            }
            System.out.printf("%d%n", q.size());
            q.element();
            System.out.printf("%d%n", q.element());
            if(q.isEmpty()) {
                System.out.printf("%s%n", "The ArrayDeque is empty");
            } else {
                System.out.printf("%d%n", q.peek());
            }
            
            System.out.printf("%d%n", q.size());
            Integer first = q.remove(),last = q.remove();
            System.out.printf("%d %d%n",first,last);
            System.out.printf("%d%n", q.size());
            
            //Map接口的实现
            Map<Integer,String> mp = new HashMap<Integer,String>();
            mp.put(1, "111");
            mp.put(2, "222");
            String tt = mp.put(3, "333");
            System.out.println(tt);        //null
            String tmp = mp.put(1, "444");
            System.out.printf("%s%n",tmp);        //111
            System.out.printf("The size of the map is %d.%n", mp.size());    //3
            for(int i=0;i<mp.size();i++) {
                System.out.printf("id=%d, value=%s%n",i+1,mp.get(i+1));
            }
            mp.remove(1);    //delete key=1
            
            Set<Integer> keys = mp.keySet();
            //foreach
            for(Integer num : keys) {
                System.out.printf(" %d", num);
            }
            //iterator
            Iterator<Integer> it1 = keys.iterator();
            while(it1.hasNext()) {
                System.out.printf(" %d", it1.next());
            }
            
            
            Collection<String> coll = mp.values();
            //foreach
            for(String s : coll) {
                System.out.printf(" %s", s);
            }
            //iterator
            Iterator<String> it2 = coll.iterator();
            while(it2.hasNext()) {
                System.out.printf(" %s", it2.next());
            }
            
            Set<Map.Entry<Integer, String>> ss = mp.entrySet();
            //foreach
            for(Map.Entry<Integer, String> pair : ss) {
                Integer num = pair.getKey();
                String value = pair.getValue();
                
                System.out.printf(" %s '+' id=%d, value=%s", pair,num,value);
            }
            //iterator
            Iterator<Map.Entry<Integer, String>> it3 = ss.iterator();
            while(it3.hasNext()) {
                System.out.printf(" %s", it3.next());
            }
            
            //TreeMap
            TreeMap<Integer,String> treemp = new TreeMap<Integer,String>(new myComparator());
            treemp.put(111,"111");treemp.put(222, "222");treemp.put(112,"112");treemp.put(113, "113");
            for(Map.Entry<Integer, String> pair : treemp.entrySet()) {
                Integer num = pair.getKey();
                String str = pair.getValue();
                System.out.printf(" %d:%s ", num,str);
            }
        }
    }
    
    class myComparator implements Comparator<Integer> {
        public myComparator() {
        }
        public int compare(Integer a,Integer b) {
            return a.compareTo(b);
        }
        
    }

下面是运行出来的结果，友友们可以对照着看，有没有初学者呀，come here and leave a message please!

10
    1
    1
    10
    1 2
    8
    null
    111
    The size of the map is 3.
    id=1, value=444
    id=2, value=222
    id=3, value=333
     2 3 2 3 222 333 222 333 2=222 '+' id=2, value=222 3=333 '+' id=3, value=333 2=222 3=333 111:111  112:112  113:113  222:222

转载于:https://www.cnblogs.com/RainingDays/p/3511083.html