通过double和String对arraylist进行排序

Question

我们被赋予了一项任务：

• 按狗尾长度排序数组列表（双）
• 如果两只或更多只狗具有相同的尾巴长度，请按名称排序

我能够创建一个代码但是在第一次打印时没有显示正确的结果。 我必须再次尝试进行实际排序。

我对编程很新，这让我很困惑。 有任何想法吗？ 谢谢！

private void listDogs() {
    boolean length = false;
    for (int i = 0; i < dogs.size(); i++) {
        length = true;
    }
    if (dogs.isEmpty()) {
        System.out.println("Error: no dogs in register");

    }else {
        System.out.println("Please enter the tail lenght minimum: ");
        double tailLength = scan.nextDouble();
        scan.nextLine();

        Collections.sort(dogs);
        for (int i = 0; i < dogs.size(); i++) {
            if (dogs.get(i).getTailLength() >= tailLength) {
                System.out.println(dogs.get(i));
                length = true;
            }
        }
        if (length == false) {
                System.out.println("Error: No dog is registered with this tail length.");   
        }       

---

@Override
public int compareTo(Dog o) {
    // TODO Auto-generated method stub
    int compare = Double.compare(tailLength, o.tailLength);   
    if (compare == 0) {
        compare = Double.compare(tailLength, o.tailLength);    
    }
    if (compare == 0) {
        compare = name.compareTo(o.name);
    }
    return compare;
}

Answer 1

我不确定这是否能解决你的问题，但你有一个问题

scan.nextLine();

在你的代码中，我不明白是否必须存在，因为据我所知它只等待你输入一些东西，然后它甚至不会将它保存在一个变量中。 所以你可能会删除这一行（第12行）。

Answer 2

你试试这个吗？

import java.util.ArrayList;
import java.util.Collections;

public class Dog implements Comparable<Dog> {

    private double tailLength;
    private String name;

    public Dog(final double _tailLength, final String _name) {
        tailLength = _tailLength;
        name = _name;
    }

    @Override
    public String toString() {
        return "Dog [tailLength=" + tailLength + ", name=" + name + "]";
    }

    @Override
    public int compareTo(final Dog o) {
        int res = Double.compare(tailLength, o.getTailLength());
        if (res == 0) {
            res = name.compareTo(o.getName());
        }
        return res;
    }

    public double getTailLength() {
        return tailLength;
    }

    public void setTailLength(final double tailLength) {
        this.tailLength = tailLength;
    }

    public String getName() {
        return name;
    }

    public void setName(final String name) {
        this.name = name;
    }

    public static void main(final String[] args) {
        final ArrayList<Dog> dogs = new ArrayList<Dog>();
        dogs.add(new Dog(2, "Dog D"));
        dogs.add(new Dog(2, "Dog A"));
        dogs.add(new Dog(5, "Dog C"));
        dogs.add(new Dog(4, "Dog A"));
        dogs.add(new Dog(3, "Dog A"));
        dogs.add(new Dog(3, "Dog B"));
        dogs.add(new Dog(1, "Dog A"));

        // Sort Dog by tailLength and name
        Collections.sort(dogs);

        final Scanner sc = new Scanner(System.in);
        while (true) {
            System.out.println("tailLength: ");
            final double inputTaillength = sc.nextDouble();
            for (final Dog dog : dogs) {
                if (dog.tailLength == inputTaillength) {
                    System.out.println(dog);
                }
            }

        }
    }
}