泡泡排序ArrayList时遇到问题

Question

我试图冒泡排序数组列表,我不断收到错误bad operand types for binary operator '>'我试图按数字顺序对它进行排序,以获得下面列出的测试分数.我是java的新手,对于该怎么做我很困惑.我很确定整数存储在列表中.

我的代码是:

 public static void sort(){
               int k = 0;
           boolean exchangeMade = true;
           while((k < classroom.size() - 1) &&exchangeMade){
              exchangeMade = false;
              k++;
              for (int j = 0; j < classroom.size() - k; j++)
                  if(classroom.get(j) > classroom.get(j+1)){
                    swap(j, j+1);
                    swap(classroom, j, j+1);
                    exchangeMade = true;
              }
          } 

该程序的其余代码是

public class Test {

  private static FileInputStream inFile;
  private static InputStreamReader inReader;
  private static BufferedReader reader;

  private static List<Student> classroom =
      new ArrayList<Student>(); // ArrayList to store the classroom.

  public static void main(String args[]) throws IOException {
    initFile();
    getData();
    System.out.print(classroom); //output of the complete class.
    sort();
    System.out.print(classroom); //output after sorting.
    inFile.close();
  }

  // preparing the file for input

  public static void initFile() throws IOException {

    inFile =
        new FileInputStream(
            "C:\\Users\\clamanna\\Google Drive\\Senior\\AP COMP SCI\\!!VHSJava\\!!APCSDATA\\truefalse.txt");
    inReader = new InputStreamReader(inFile);
    reader = new BufferedReader(inReader);
  }

  //  Separate the id from the answers and store the answers in an array.

  public static void getData() throws IOException {
    String line = reader.readLine(); //Seed

    String[] answerkey = new String[10]; //Store the answer key from the first line of the txt file.

    for (int i = 0;
        i < answerkey.length;
        i++) { // take that line and place each answer in an array.

      answerkey[i] = line.substring(i, i + 1);
    }

    line = reader.readLine(); // read the following line of the txt file.

    while (line != null) // Read and create a student for each line.
    {
      String[] answers = new String[10];
      StringTokenizer strTkn = new StringTokenizer(line);
      String id = strTkn.nextToken();
      String answerline = strTkn.nextToken();

      for (int i = 0; i < answers.length; i++) {

        answers[i] = answerline.substring(i, i + 1);
      }

      Student stu = new Student(id, answers);

      stu.grade(answerkey, answers);

      classroom.add(stu);

      line = reader.readLine(); //updating what is being read
    }
  }
}

Answer 1

关系运算符喜欢>和<仅定义数字基元类型,如int和double.

您还可以使用它们相当于盒装类型,如Integer和Double,因为这些可以自动拆箱到原语.

要比较对象,您应该使用以下Comparable.compareTo方法:

classroom.get(j).compareTo(classroom.get(j+1)) > 1

注意,这需要你的元素来实现Comparable接口-这常见的类型,如Integer,Double等做的,以及之类的东西String(这与字典顺序一致实现它).

如果您的元素类没有实现Comparable(并且您无法对其进行更改以实现它),则可以使用Comparable被调用的"外部"形式Comparator,这是这样的接口:

interface Comparable<T> {
  int compare(T a, T b);
}

你不加入,你想比较类-你实现这个接口作为一个单独的类,这样compare如果你考虑返回负数,零或正数a < b,a == b并a > b分别.

然后,你会使用:

comparator.compare(classroom.get(j), classroom.get(j + 1)) > 1

where comparator是实现类的实例Comparator<Student>.(实际上,它可以Comparator<? super Student>,但现在不要担心太多).