代码语言：java复制
public class MyListDemo {
public static void main(String[] args) {
List<BigDecimal> lis = new ArrayList<BigDecimal>();
lis.add(new BigDecimal(123.23));
lis.add(new BigDecimal(12.1));
lis.add(new BigDecimal(122.2));
lis.add(new BigDecimal(3.23));
lis.add(new BigDecimal(23.23));
// BigDecimal 计算
BigDecimal nu = lis.stream().reduce(BigDecimal.ZERO, BigDecimal :: add);
System.out.println("BigDecimal : " nu);
List<Double> list = new ArrayList<Double>();
list.add(12.1);
list.add(12.2);
list.add(12.3);
list.add(12.4);
Optional<Double> num = list.stream().reduce((x,y)->x y);
// 基本数字类型计算
Double sum2=list.stream().reduce((double) 0,(x,y)->x y);
System.out.println("double : " num);
System.out.println(sum2);
List<String> lists = new ArrayList<>();
lists.add("ddd");
lists.add("aaa");
lists.add("bbb");
lists.add("nnn");
lists.add("ddd");
// 遍历
lists.forEach(e -> {
System.out.println("遍历 ： " e);
});
// 去重
List<String> aa = lists.stream().distinct().collect(Collectors.toList());
System.out.println("去重：" aa.toString());
// 排序
List<String> sa = lists.stream().sorted().collect(Collectors.toList());
System.out.println("排序：" sa.toString());
// 转大写
List<String> ss = lists.stream().map(String::toUpperCase).collect(Collectors.toCollection(ArrayList::new));
System.out.println("转大写：" ss.toString());
List<User> li = new ArrayList<>();
li.add(new User("123", 321.0));
li.add(new User("3", 321.1));
li.add(new User("23", 321.2));
double NUM = li.stream().map(User :: getNum).reduce(0.0, (X,Y) -> (X Y));
System.out.println("实体类属性计算：" NUM);
List<Double> numList = li.stream().map(User :: getNum).collect(Collectors.toList());
System.out.println("得到user中num属性集合" numList.toString());
Map<String,Object> maps = li.stream().collect(Collectors.toMap(User :: getKey, User :: getNum));
System.out.println("list转map值为某个属性： " maps.toString());
Map<String,Object> maps1 = li.stream().collect(Collectors.toMap(User :: getKey, user -> user));
System.out.println("list转map值为实体类： " maps1.toString());
List<Map<String,Object>> l = new ArrayList<>();
Map<String,Object> ma = new HashMap<String, Object>();
ma.put("123", 321);
Map<String,Object> ma1 = new HashMap<String, Object>();
ma1.put("123", 21);
Map<String,Object> ma2 = new HashMap<String, Object>();
ma2.put("123", 1);
Collections.addAll(l, ma,ma1,ma2);
// l.stream().map(str -> str.get("123"));
// 取某个key 值为键，当前map为值得到新集合
Map<Object, Object> ls = l.stream().collect(Collectors.toMap( map -> map.get("123"),key -> key));
System.out.println("list集合得到一个新的map: " ls.toString());
// 根据实体类某个值去重得到信息list
List<User> lt = new ArrayList<User>();
lt.add(new User("1", 23.9));
lt.add(new User("1", 22.9));
lt.add(new User("2", 23.8));
lt.add(new User("3", 23.1));
List<User> unilt = lt.stream().collect(Collectors.collectingAndThen(
Collectors.toCollection(() -> new TreeSet<>(Comparator.comparing(User::getKey))), ArrayList::new));
System.out.println("根据实体类中的某个值进行去重：" unilt.toString());
// 条件过滤
List lsd = lt.stream().filter(user -> user.getKey().equals("1")).collect(Collectors.toList());
System.out.println(lsd.toString());
// 多条件过滤
long count = lt .stream().filter( e-> e.getKey().equals("1")).filter(e -> e.getNum() == 23.9).count();
System.out.print(count);
Map<String,Double> map = new HashMap<>();
map.put("1_U",1.1);
map.put("5_U",1.5);
map.put("2_U",1.2);
map.put("3_U",1.3);
map.put("4_U",1.4);
// 取值最大
Optional<Double> value = map.values().stream().max(Comparator.comparing(Double::doubleValue));
Double v = value.get();
System.out.println(v);
// 取值最小的
Optional<Double> ma = map.entrySet().stream().map(k -> k.getValue()).min(Comparator.comparing(Double::doubleValue));
System.out.println(ma.get());
// 根据最大的值返回key
Optional<Map.Entry<String, Double>> m = map.entrySet().stream().filter(k -> k.getValue() == v).findAny();
System.out.println(m.get().getKey());
}
}
}
package javaDemo.threadLocal;
public class User {
private String key;
private Double num;
public User(String key,Double num) {
this.key = key;
this.num = num;
}
/**
* @return key
*/
public String getKey() {
return key;
}
/**
* @param paramtheparamthe{bare_field_name} to set
*/
public void setKey(String key) {
this.key = key;
}
/**
* @return num
*/
public Double getNum() {
return num;
}
/**
* @param paramtheparamthe{bare_field_name} to set
*/
public void setNum(Double num) {
this.num = num;
}
@Override
public String toString() {
return "User [key=" key ", num=" num "]";
}
}
