如何在不使用 java 中的 compare() 方法的情况下进行选择排序？

Question

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我最近开始在学校学习java，其中一个任务是创建一种排序方法，如选择排序或插入排序，而不使用java自己的内置函数。我在网上看了很多，我发现的所有方法都是针对Arrays而不是ArrayLists的。分配的目标是按照尾巴长度对狗类进行排序，如果狗的尾巴长度相同，也按照名称排序。 到目前为止，这就是我所做的；

狗类

public class Dog {
private static final double DEFAULT_TAIL_SIZE = 10.0;
private static final double DEFAULT_TAX_SIZE = 3.7;
private static int count;
private String name;
private String breed;
private int age;
private int weight;
private double tailLenght;


public Dog(String name, String breed, int age, int weight) {
    //count++;
    this.name = name;
    this.age = age;
    this.breed = breed;
    this.weight = weight;
    this.tailLenght = tailLenght;

}

public String getName() {
    return name;
}

public int getAge() {
    return age;
}

public String getBreed() {
    return breed;
}

public int getWeight() {
    return weight;
}

public void setAge(int age) {
    age = age <= 0 ? 1 : age;
}

public double getTailLength() {
    if (breed.equals("Tax") || breed.equals("dachshund")||breed.equals("tax") || breed.equals("Dachshund")) {
        return tailLenght = DEFAULT_TAX_SIZE;
    } else {
        return tailLenght = age * weight/DEFAULT_TAIL_SIZE;
    }

}
@Override
public String toString() {
    //System.out.println(String.format("name=%s breed=%s age=%d weight=%d taillenght=%.1f", name, breed, age, weight, getTailLength()));
    return name + " " + breed + " " + age + " " + weight + " " + getTailLength();
}

这是我制作的排序代码，由于代码使用内置的 java 排序方法而未被接受。 这是我在此次作业期间唯一可以编辑的代码

public class DogSorter {

public void sort(ArrayList<Dog> dogs) {
    dogs.sort(new Comparator<Dog>() {
        @Override
        public int compare(Dog d1, Dog d2) {
            int comparison = 0;
            comparison = Double.valueOf(d1.getTailLength()).compareTo(d2.getTailLength());
            if (comparison == 0) {
                comparison = String.valueOf(d1.getName()).compareTo(d2.getName());
            }
            return comparison;

        }

    });
}

最后这是我们从老师那里收到的跑步者代码

  import java.util.ArrayList;
import java.util.Random;

public class DogSorterRunner {
    private static final int NUMBER_OF_DOGS = 12;

private static final Random RND = new Random();
private static final String[] NAMES = { "Fido", "Karo", "Molly", "Bella", "Wilma", "Doris", "Sigge", "Charlie",
        "Ludde", "Bamse", "Lassie", "Ronja", "Ratata", "Maki", "Dora", "Luna", "Spike", "Mumsan", "Cherie" };

private static final String[] BREEDS = { "Labrador", "Golden retriever", "Tax", "Dachshund" };

private static String getRandomValueFromArray(String[] array) {
    return array[RND.nextInt(array.length)];
}

private static String randomName() {
    return getRandomValueFromArray(NAMES);
}

private static String randomBreed() {
    return getRandomValueFromArray(BREEDS);
}

private static int randomNumber() {
    return RND.nextInt(10) + 1;
}

public static void main(String[] args) {
    ArrayList<Dog> dogs = new ArrayList<>();

    for (int n = 0; n < NUMBER_OF_DOGS; n++) {
        Dog dog = new Dog(randomName(), randomBreed(), randomNumber(), randomNumber());
        dogs.add(dog);
    }

    new DogSorter().sort(dogs);

    for (Dog dog : dogs) {
        System.out.println(dog);
    }
}

任何帮助和反馈将不胜感激！

Answer 1

赋值的重点是你应该自己实现selection或insertion排序，而不是使用Java内置的排序功能。这就是您在实现排序算法方面展示一些知识的方式。

这是一个选择排序的示例，它基于您的条件（尾部和名称），应该让您了解函数的外观。做一些练习，我建议你尝试自己实现插入排序。

public class DogSorter {

    public void sort(ArrayList<Dog> dogs) {
        dogs.sort(new Comparator<Dog>() {
            @Override
            public int compare(Dog d1, Dog d2) {
                int comparison = 0;
                comparison = Double
                        .valueOf(d1.getTailLength())
                        .compareTo(d2.getTailLength());
                if (comparison == 0) {
                    comparison = String
                            .valueOf(d1.getName())
                            .compareTo(d2.getName());
                }
                return comparison;
            }
        });
    }

    public void selectionSort(ArrayList<Dog> dogs) {
        int n = dogs.size();

        // One by one move boundary of unsorted subarray
        for (int i = 0; i < n - 1; i++) {
            // Find the minimum element in unsorted array
            int min_idx = i;
            for (int j = i + 1; j < n; j++) {
                Dog d1 = dogs.get(j);
                Dog d2 = dogs.get(min_idx);
                int comparison = Double
                        .valueOf(d1.getTailLength())
                        .compareTo(d2.getTailLength());
                if (comparison == 0) {
                    comparison = String
                            .valueOf(d1.getName())
                            .compareTo(d2.getName());
                }
                if (comparison < 0)
                    min_idx = j;
            }

            // Swap the found minimum element with the first
            // element

            // using built in swap
            // Collections.swap(dogs, min_idx, i);

            // using classic temp method
            Dog temp = dogs.get(min_idx);
            dogs.set(min_idx, dogs.get(i));
            dogs.set(i, temp);

            // using classic method without temp element
            // dogs.set(i, dogs.set(min_idx, dogs.get(i)));
        }
    }
}

这里也是一个repl，在实践中可以看到这个函数：https://repl.it/repls/VividMeekPlans