对象Java arraylist的order字段

Question

我有一个包含对象字段 4 的数组列表。我需要知道如何使用执行算法的通用方法（isort、msort、qsort）“一个接一个”地对对象的字段进行排序。

我知道比较器接口，但不知道如何检查泛型类型 T 中的所有字段。

Answer 1

如果我的理解正确，您有一个用作泛型类型的类，并且想知道如何使用 Comparator 接口。这是我的尝试：

class ClassWithFields {

    int fieldA;
    double fieldB;
    String fieldC;

    public ClassWithFields(int fieldA, double fieldB, String fieldC) {
        this.fieldA = fieldA;
        this.fieldB = fieldB;
        this.fieldC = fieldC;
    }

    @Override
    public String toString() {
        return "["+fieldA+","+fieldB+","+fieldC+"]";
    }

}

public class GenericComparator<T extends ClassWithFields> implements Comparator<T> {

    @Override
    public int compare(T o1, T o2) {
        if (o1.fieldA < o2.fieldA)
            return -1;
        else if (o1.fieldA > o2.fieldA)
            return +1;
        else if (o1.fieldB < o2.fieldB)
            return -1;
        else if (o1.fieldB > o2.fieldB)
            return +1;
        else
            return o1.fieldC.compareTo(o2.fieldC);
    }

    public static void main(String[] args) {
        ClassWithFields[] cwfArray = new ClassWithFields[3];
        cwfArray[0] = new ClassWithFields(2, 1.5, "Test");
        cwfArray[1] = new ClassWithFields(1, 3.5, "Test");
        cwfArray[2] = new ClassWithFields(2, 1.5, "Tast");
        Arrays.sort(cwfArray, new GenericComparator<ClassWithFields>());
        System.out.println(Arrays.toString(cwfArray));
    }

}

当你运行 main 方法时，第一个数组项将被放在数组的后面，因为 1

编辑：现在应该这样做了。

public class GenericComparator<T extends ClassWithFields> implements Comparator<T> {

    private String fieldIdentifier;

    public GenericComparator(String fieldIdentifier)
    {
        this.fieldIdentifier = fieldIdentifier;
    }

    @Override
    public int compare(T o1, T o2) {
        if (fieldIdentifier.equals("fieldA")) {
            if (o1.fieldA < o2.fieldA)
                return -1;
            else if (o1.fieldA > o2.fieldA)
                return +1;
            return 0;
        }
        else if (fieldIdentifier.equals("fieldB")) {
            if (o1.fieldB < o2.fieldB)
                return -1;
            else if (o1.fieldB > o2.fieldB)
                return +1;
            return 0;
        }
        else
            return o1.fieldC.compareTo(o2.fieldC);
    }

    public static <S extends ClassWithFields> void isort(ArrayList<S> array, String type) {
        Comparator<S> comp = new GenericComparator<S>(type);
        // TODO employ search algorithm
        S help = null;
        for (int i = 0; i < array.size(); i++) {
            for (int j = 0; j < array.size(); j++) {
                if (comp.compare(array.get(i), array.get(j)) > 0) {
                    help = array.get(i);
                    array.set(i, array.get(j));
                    array.set(j, help);
                }
            }
        }
    }

    public static void main(String[] args) {
        ClassWithFields[] cwfArray = new ClassWithFields[3];
        cwfArray[0] = new ClassWithFields(2, 1.5, "Test");
        cwfArray[1] = new ClassWithFields(1, 3.5, "Test");
        cwfArray[2] = new ClassWithFields(2, 1.5, "Tast");
        ArrayList<ClassWithFields> cwfList = new ArrayList<ClassWithFields>();
        Collections.addAll(cwfList, cwfArray);
        isort(cwfList, "fieldA");
        System.out.println(Arrays.toString(cwfList.toArray()));
    }

}