Java8之List转换

• List转换成map

  public static void listConversionToMap(List list) {
      //颜色作为key，重量作为value,如果key重复，取较重的值（注意：key重复不做处理会报-->java.lang.IllegalStateException: Duplicate key）
      Map colorForWeight = list.stream().collect(Collectors.toMap(Orange::getColor,
              Orange::getWeight, (oldValue, newValue) -> oldValue > newValue ? oldValue : newValue));
  
      //颜色作为key,Orange为value
      Map colorForOrange = list.stream().collect(Collectors.toMap(Orange::getColor,
              (orange) -> orange, (oldValue, newValue) -> oldValue.getWeight() > newValue.getWeight() ? oldValue :
                      newValue));
  
      //已颜色作为key进行分组
      Map> colorForOranges = list.stream().collect(Collectors.groupingBy(Orange::getColor));
  }
  

• List转换成Set

  public static void listConversionToSet(List list) {
      list.stream().collect(Collectors.toSet());
  }
  
  //将实体中的某属性转换为set
  public static void listConversionToSet(List list) {
      Set colorSet = list.stream().map((orange) -> orange.getColor()).collect(Collectors.toSet());
  }
  

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