//HashMap类常用函数Map map = new HashMap<Character, Integer>(); //char对应包装类是 Character，不用Stringfor(int k=0;k<26;k++){map.put((char)(k+97), 0);}Set keys = map.keySet(); //键值集合System.out.println(keys);//[f, g, d, e, b, c, a, n, o, l, m, j, k, h, i, w, v, u, t, s, r, q, p, z, y, x]int cnt = (int) map.get('d');System.out.println(cnt);exist = map.containsKey('A');System.out.println(exist); //not eixstexist = map.containsValue(0);System.out.println(exist); //existCollection res = map.values(); //Value集合map.remove('a'); map.put('a',1); //两步，实现更新'a'的统计值map.size();map.isEmpty();//map.clear();//遍历键，通过键取值Set set = map.keySet();for (Object key : set) {System.out.println("键:"+key+" 值:"+map.get(key));}//遍历键集合Iterator it=map.keySet().iterator();while(it.hasNext()){System.out.println("键:"+it.next());}//遍历键值集合Iterator it2=map.entrySet().iterator();while(it2.hasNext()){System.out.println(it2.next());}
//ArrayList类常用函数int[] input0 = {2,3,4,5,7,4,5};ArrayList out = new ArrayList(); for(int i = 0; i< input0.length;i++){out.add(input0[i]);}System.out.println("res——"+out);//res——[2, 3, 4, 5, 7, 4, 5]System.out.println(out.subList(2, 4));//[4,5], 前开后闭的序号切片取值Set test = new HashSet(out); //以List为参数构造Set对象System.out.println(test.size());Set in = new HashSet(); //以Set为参数构造List对象in.add(3);in.add(1);in.add(4);List test2 = new ArrayList(in);System.out.println(test2.size());int pos = out.indexOf(5);if(pos == -1){//if(arr.contains(5))System.out.print("not exist");}else{System.out.println("exist,pos="+pos+",last_pos="+out.lastIndexOf(5)); //返回第一个出现的元素}Object[] out_ = out.toArray(); //ArrayList转换成Object数组，具体操作某元素再进行转型//String中常用函数Integer.parseInt("10");String str = "hello-world";String[] strs = str.split("-"); System.out.println(strs[0]+","+strs[1]);String _stra = str.concat("!");System.out.println(_stra+","+str);byte[] bytes = str.getBytes();char[] chars = str.toCharArray();int index = str.indexOf("world");System.out.println(index);boolean exist = str.endsWith("!");boolean first_ = str.startsWith("he");System.out.println(first_+","+exist);System.out.println("hellohello".indexOf("hello")+","+("hellohello".lastIndexOf("hello"))); //0,5//Arrays类常用函数int[] data = {2,3,4,4,4,4,5};List arr = Arrays.asList(data); //将普通数组转成成ListSystem.out.println(arr);//int size = arr.size();//for(int k =0 ; k < size;k++){//System.out.println(arr.get(k));//}Arrays.sort(data); //Arrays.XXX(arr) 静态函数参数都是简单数组，不可以是Listfor(int item : data){System.out.println(item);}Arrays.binarySearch(data, 8);Arrays.copyOfRange(data, 3, 6);
