数组列表中的Java分组值

Question

我有 3 个类:

1. Calculation class (includes FinalPrice() method which is return with a double value)
2. File Reader class (Load CSV file, split data into an array and return with the first element of the array, which is a String. Includes getType() method)
3. Contract class(only contains a constructor)

File a = new File("D:\\...\\contract.csv"); Calculation1 calc = new Calculation1(a); File_Reader1 b = new File_Reader1(); Contract c = new Contract(b.getType(a),calc.FinalPrice());

我需要一个列表来存储 Contract 对象并对键进行分组(即 b.getType(a) )并对它们的值求和(即 calc.FinalPrice() )，例如

输入(例如):

list.add("AB", 5); list.add("AC", 8); list.add("AB", 12);

我想得到这样的输出:

"AB" : 17 "AC" : 8

谁能帮帮我？

Answer 1

在 Java 8 中，

 entries.stream().collect(Collectors.groupingBy(
      entry -> entry.getKey(),
      Collectors.summingInt(entry -> entry.getValue())));