知识分享刚起步,愿意分享工作中遇到的一些问题
Java中遍历问题
1.java中List<Map<String,Object>>遍历的方法
List<Map<String, Object>> listMaps = new ArrayList<Map<String, Object>>();
for (Map<String, Object> map : listMaps) {
for (String s : map.keySet()) {
System.out.print(map.get(s) + " ");
}
}
2.List<Map<String,Object>> listMap= null;
for(int i = 0; i<len; i++){
Map<String,Object> map1 = listMap.get(i);
for (Object o : map1.keySet()) {
System.out.print("key=" + o + " value=" + mapMax.get(o));
}
}
3.List<Map<String,Object>> resultList=new ArrayList<Map<String,Object>>();
for (Map<String, Object> map : resultList) {
for (String s : map.keySet()) {
System.out.print( map.get(s) );
}
}
4.List<Object[]> list= new ArrayList<Object[]>();
for (Object[] qwe : list) {
System.out.print("list[0]"+qwe[0]);
System.out.print("list[1]"+qwe[1]);
}
5.遍历一维数组 Int[] arr = {1,2,3,4,5};
①.for循环遍历
for(int i=0;i<arr.length;i++){
System.out.println( arr[i] );
}
②.将数组转换为字符串输出
System.out.println( Arrays.toString(arr) );
③.使用foreach循环遍历数组
for( int a : arr ){
System.out.println( a + “” );
}
6.遍历二维数组
public static void main(String args[]) {
int arr[][] = { { 1 }, { 2, 3 }, { 4, 5, 6 }, { 7, 8, 9, 10 } };
①.方法一
for (int x = 0; x < arr.length; x++) {
for (int y = 0; y < arr[x].length; y++) {
System.out.print(arr[x][y] + ",");
}
System.out.println("");
}
②.方法二
//遍历二维数组中每一个一维数组
for(int[] cells : arr) {
//遍历一维数组中每一个元素
for(int cell : cells) {
System.out.print(cell+" ");
}
System.out.println();
}
}
7.遍历Map对象 Map<Integer, Integer> map = new HashMap<Integer, Integer>();
//遍历map中的键
for (Integer key : map.keySet()) {
System.out.println("Key = " + key);
}
//遍历map中的值
for (Integer value : map.values()) {
System.out.println("Value = " + value);
}
//键值都需要时使用
for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
}
8.HashMap的遍历
1.使用迭代器
Map map = new HashMap();
Iterator iter = map.entrySet().iterator();
while (iter.hasNext()) {
Map.Entry entry = (Map.Entry) iter.next();
Object key = entry.getKey();
Object val = entry.getValue();
}
2.for each遍历
Map<String, String> map = new HashMap<String, String>();
①.for (String key : map.keySet()) {
map.get(key);
}
②.for (Entry<String, String> entry : map.entrySet()) {
entry.getKey();
entry.getValue();
}
9.Set集合的遍历
①.迭代遍历:
Set<String> set = new HashSet<String>();
Iterator<String> a= set.iterator();
while (a.hasNext()) {
String str = a.next();
System.out.println(str);
}
②.for循环遍历:
for (String str : set) {
System.out.println(str);
}
③.set为object类型
Set<Object> set = new HashSet<Object>();
for(Object obj: set) {
if (obj instanceof Character) {
char chr = (Character)obj;
System.out.println("for: "+chr);
}
}