Map集合的定义
数组的元素类型是Node<K,V>，Node<K,V>继承自Map.Entry<K,V>，表示键值对映射。
static class Node<K,V> implements Map.Entry<K,V> {
final int hash;
final K key;
V value;
Node<K,V> next;
//构造函数 ( Hash值键值下一个节点 )
Node(int hash, K key, V value, Node<K,V> next) {
this.hash = hash;
this.key = key;
this.value = value;
this.next = next;
}
public final K getKey() { return key; }
public final V getValue() { return value; }
public final String toString() { return key + "=" + value; }
public final int hashCode() {
return Objects.hashCode(key) ^ Objects.hashCode(value);
}
public final V setValue(V newValue) {
V oldValue = value;
value = newValue;
return oldValue;
}
public final boolean equals(Object o) {
if (o == this)
return true;
if (o instanceof Map.Entry) {
Map.Entry<?,?> e = (Map.Entry<?,?>)o;
if (Objects.equals(key, e.getKey()) &&
Objects.equals(value, e.getValue()))
return true;
}
return false;
}
}Map集合的初始化
value存数组
HashMap<Integer,String[]> columnValueList = new HashMap<Integer,String[]>();
HashMap<String,String> primaryMap = new HashMap<String,String>();
primaryMap.put(fieldName, fieldOrder.toString());
String[] columnValue = new String[3];
columnValue[0]=fieldName;
columnValue[2]=fieldDataType;
columnValueList.put(fieldOrder-1,columnValue);value存不同类型的集合
List<HashMap<String, Object>> dataList = new ArrayList<HashMap<String, Object>>();
HashMap<String, Object> Data = new HashMap<String, Object>();
String ageId = null;
String sql ="select * from gl a where substr(a.xl_time,0,10)=to_char(sysdate,'yyyy-mm-dd') and a.user=?";
List<IBean> IBeans = query(sql,userId);
for(int i=0;i<IBeans.size();i++){
ageId = String.valueOf(ryIBeans.get(i).get("ID"));
List<IBean> cList = (List<IBean>) Data.get(coverageId);
if(cList==null){
cList = new ArrayList<IBean>();
}
cList.add(IBeans.get(i));
Data.put(coverageId,cList);
}
Set<String> keys = Data.keySet();
pointData.put("pointsKey", keys);
dataList.add(Data);
dataList.add(intData);
return dataList;
}一、iterator()遍历Map集合
1、for循环遍历
StringBuilder updateSqlValue = new StringBuilder();
HashMap<Integer,String[]> columnValueList = new HashMap<Integer,String[]>();
StringBuilder paramkey=new StringBuilder();
StringBuilder paramval=new StringBuilder();
HashMap<String,String> primaryMap = new HashMap<String,String>();
for (Iterator<Entry<Integer, String[]>> it = columnValueList.entrySet().iterator(); it.hasNext(); ) {
Entry<Integer, String[]> entry = (Entry<Integer, String[]>) it.next();
String[] entryValue = entry.getValue();
paramkey.append(",").append(entryValue[0]);
paramval.append(",").append(entryValue[1]);
}
for (Iterator<Entry<String, String>> pm = primaryMap.entrySet().iterator(); pm.hasNext(); ) {
Entry<String, String> entry = (Entry<String, String>) pm.next();
if(templateActionField == null){
paramPrimarykey.append(",").append(entry.getKey());
String pkVal = CommonUtils.getUUID();
paramSubval.append(",").append("'"+pkVal+"'");
primaryMapVal.add(pkVal);
}2、while遍历
public static void main(String[] args) {
HashMap<String,Student> hashMap=new HashMap<String,Student>();
hashMap.put("1号", new Student("张三",10));
hashMap.put("2号", new Student("李四",11));
hashMap.put("3号", new Student("王五",12));
Student s=hashMap.get("1号");
System.out.println(s);
Iterator<String> it=hashMap.keySet().iterator(); // 获取key的集合 ，再获取迭代器
while(it.hasNext()){
String key=it.next(); // 获取key
Student student=hashMap.get(key); // 获取值
System.out.println("key="+key+",value="+student);
}
}二、entrySet()遍历map集合
Map<String, List<FastEntryVO>> fastEntryMap = getFastEntryDtoMap(fastEntryList);
List<FastEntryDto> fastEntryDtoList = new ArrayList<FastEntryDto>(1);
FastEntryDto fastEntryDto = null;
for (Map.Entry<String, List<FastEntryVO>> entry : fastEntryMap.entrySet())
{
for (FastEntryVO fastEntry : fastEntryList)
{
if (fastEntry.getFastEntryId().equals(entry.getKey()))
{
fastEntryDto = new FastEntryDto();
BeanUtils.copyProperties(fastEntry, fastEntryDto);
fastEntryDto.setFastEntryList(entry.getValue());
fastEntryDtoList.add(fastEntryDto);
break;
}
}
}
return fastEntryDtoList;
}
private Map<String, List<FastEntryVO>> getFastEntryDtoMap(List<FastEntryVO> fastEntryList) {
Map<String, List<FastEntryVO>> entryMap = new HashMap<String, List<FastEntryVO>>(1);
List<FastEntryVO> secondEntryList = null;
FastEntryVO entry = null;
for (FastEntryVO fastEntry : fastEntryList) {
if (fastEntry.getParentId().equals("-1")) {
continue;
}
entry = new FastEntryVO();
BeanUtils.copyProperties(fastEntry, entry);// 复制属性
if (entryMap.containsKey(fastEntry.getParentId())) {
secondEntryList = entryMap.get(fastEntry.getParentId());
secondEntryList.add(entry);
} else {
secondEntryList = new ArrayList<FastEntryVO>(1);
secondEntryList.add(entry);
entryMap.put(fastEntry.getParentId(), secondEntryList);
}
}
return entryMap;
}Map集合的基本方法
方法的使用
public List<CheckAdvice> removePicExtra(List<CheckAdvice> picList,List<CheckAdvice> list) {
List<CheckAdvice> newList= new ArrayList<CheckAdvice>();
HashMap<String, String> hashMap = new HashMap<String, String>();
for (CheckAdvice checkAdvice : picList) {
if (checkAdvice == null) {
continue;
}
String adviceId = checkAdvice.getAdviceId();
if (adviceId != null) {
String value = hashMap.get(adviceId);
if (StringUtil.isEmpty(value)) { //如果value是空的 说明取到的这个adviceId是第一次取到
hashMap.put(adviceId, adviceId);
} else {
continue;
}
}
}
for (CheckAdvice checkAdvice : list) {
if (checkAdvice == null) {
continue;
}
String adviceId = checkAdvice.getAdviceId();
if (adviceId != null) {
String value = hashMap.get(adviceId);
if (StringUtil.isEmpty(value)) { //如果value是空的 说明取到的这个adviceId是第一次取到
hashMap.put(adviceId, adviceId);
newList.add(checkAdvice);
} else {
continue;
}
}
}
hashMap.clear();
return newList;
}源码
HashMap的put操作。
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
boolean evict) {
Node<K,V>[] tab; Node<K,V> p; int n, i;
if ((tab = table) == null || (n = tab.length) == 0)
n = (tab = resize()).length; //如果没有初始化则初始化table
if ((p = tab[i = (n - 1) & hash]) == null)
//这里 (n-1)&hash 是根据hash值得到这个元素在数组中的位置（即下标）
tab[i] = newNode(hash, key, value, null);
//如果数组该位置上没有元素，就直接将该元素放到此数组中的该位置上
else {
Node<K,V> e; K k;
//第一节节点hash值同，且key值与插入key相同
if (p.hash == hash &&
((k = p.key) == key || (key != null && key.equals(k))))
e = p;
else if (p instanceof TreeNode)
//属于红黑树处理冲突
e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
else {
/链表处理冲突
for (int binCount = 0; ; ++binCount) {
if ((e = p.next) == null) {
p.next = newNode(hash, key, value, null);
if (binCount >= TREEIFY_THRESHOLD - 1) // -1 for 1st
//新增节点后如果节点个数到达阈值，则将链表转换为红黑树
treeifyBin(tab, hash);
break;
}
if (e.hash == hash &&
((k = e.key) == key || (key != null && key.equals(k))))
break;
p = e;
}
}
//更新hash值和key值均相同的节点Value值
if (e != null) { // existing mapping for key
V oldValue = e.value;
if (!onlyIfAbsent || oldValue == null)
e.value = value;
afterNodeAccess(e);
return oldValue;
}
}
++modCount;
if (++size > threshold)
resize();
afterNodeInsertion(evict);
return null;
}
HashMap的get操作。
final Node<K,V> getNode(int hash, Object key) {
Node<K,V>[] tab; Node<K,V> first, e; int n; K k;
if ((tab = table) != null && (n = tab.length) > 0 &&
(first = tab[(n - 1) & hash]) != null) {
if (first.hash == hash && // always check first node
((k = first.key) == key || (key != null && key.equals(k))))
return first;
if ((e = first.next) != null) {
//如果第一个节点是TreeNode,说明采用的是数组+红黑树结构处理冲突
//遍历红黑树，得到节点值
if (first instanceof TreeNode)
return ((TreeNode<K,V>)first).getTreeNode(hash, key);
do {
if (e.hash == hash &&
((k = e.key) == key || (key != null &&
key.equals(k))))
return e;
} while ((e = e.next) != null);
}
}
return null;
}