Java 类型转化

String Double

1. String转Double

String a="8.58";
//1
Double b0= new Double（a）;
//2
double b1=Double.valueOf(a);
//3(首选)
double b2=Double.parseDouble(a);
System.out.println("b0 : "+b0+"b1 : "+b1+" "+"b2 : "+b2);

2. Double 转 String

Double a = 400.40;
//1.最简单
String b0 = "" + a;
//2
String b1= String.valueOf(a);
//3
String b2 = a.toString（）;
//4 b3包含最多3个小数点的double值。“f”用于格式化浮点数
 String b3= String.format（“％。3f”，a）;

BigDecimal Long

1. BigDecimal 转 Long

		BigDecimal b = new BigDecimal(12);
        Long c = b.longValue();

2. Long 转 BigDecimal

Long a = 1L;
BigDecimal b = new BigDecimal(a);

String List

1.String 转 List

import java.util.Arrays;
List<String> list = Arrays.asList(str.split(","));

List<String> list = Arrays.asList(StringUtils.split(str, ","));

//转list并且转换类型 searchId = "[1,2,3]"
List<Long> searchIds = Arrays.stream(sList.getSearchId()
                                        .substring(1,sList.getSearchId().length()-1).split(","))
                                        .map(s->Long.parseLong(s.trim())).collect(Collectors.toList());

2. List 转 String

import cn.hutool.core.util.StrUtil;
String str = StrUtils.join(list, ",");

String str = StringUtils.json(list.toArray(), ",");　

String str = String.join(",", list);　　

Collection 转 List

Collection<T> collection = map.values();
List<T> list = new  ArrayList<>(collection);

List 转 Set

1、set转List

Set<String>set = new HashSet<String>();
set.add("c");
set.add("d");
set.add("a");
set.add("a");
 
 
//方法一：
List<String>list = new ArrayList<String>(set);
for(Strings : list) {
    System.out.println(s);
}
System.out.println();
 
 
//方法二：
List<String>list2 = new ArrayList<String>();
list2.addAll(set);
for(Strings : list2) {
    System.out.println(s);
}

2、List 转 set

List<String>list = new ArrayList<String>();
list.add("c");
list.add("d");
list.add("a");
list.add("a");
 
 
//方法一：
Set<String>set = new HashSet<String>(list);
for(Strings : set) {
    System.out.println(s);
}
 
System.out.println();
 
 
 
//方法二：
Set<String>set2 = new HashSet<String>();
set2.addAll(list);
for(Strings : set2) {
    System.out.println(s);
}

Object 转 map

QueryRequest queryRequest = new QueryRequest();

TreeMap<String,String> params = JSONObject.parseObject(JSON.toJSONString(queryRequest),
                    new TypeReference<TreeMap<String,String>>(){});

object转指定类

Object userLoginInfo = session.getAttribute(“userLoginInfo”);
TfActivityLogin newUserLoginInfo= JSONObject.parseObject(JSONObject.toJSONString(userLoginInfo), TfActivityLogin.class);

List

List<Map<String, Object>> resultMap = dao.get();
JSONArray jsonArray = JSONUtil.parseArray(resultMap);
List<xxxVO> xxxVO = jsonArray.toList(xxxVO.class);