Fastest way to sort an array of objects in java

问题

I have a Class called apple which contains 3 values as int x, int y and int weight. Then i created an array of apple type objects. Now i want to sort the the array of objects based on weight meaning the the apple object with the lowest weight should be first and so on.

I know there are quite a few ways to achieve this by using Arrays.sort etc or comparators.

I was wondering what is the fastest way of doing this sort in Java? There can be a case where i have 500,000 objects so i want to know which sort i should use, more importantly which approach will give me best approach. i have even wrote my own quick sort with Hoare partition.

Code for Apple class

public class Apple {
    public int x;
    public int y;
    public int weight;

    public Apple(int a, int b, int w) {
        x = a;
        y = b;
        weight = w;
    }
}

Code for main class

public class main {
    static Apple[] appleArray;

    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int size = sc.nextInt();
        int totalApples = sc.nextInt();
        appleArray = new Edge[totalApples];
        int x = 10;
        int y = 20;
        int w = 30;

        for (int i = 0; i < size; i++) {
            appleArray[i] = new Apple(x, y, w);
            x++;
            y++;
            w++;
        }
        //Now i want to sort array of apple objects based on weight
    }
}

回答1:

This book has a useful cheat sheet for deciding the optimal sort for your needs: https://www.safaribooksonline.com/library/view/algorithms-in-a/9780596516246/ch04s09.html

The easiest solution

The Arrays.sort command uses a quicksort implementation, which is suitable for many situations. For your example code this might be:

Arrays.sort(appleArray, new Comparator<Apple>(){  
    @Override  
    public int compare(Apple apple1, Apple apple2){  
         return apple1.weight - apple2.weight;  
    }  
});

The fastest solution

In your case you have a large array containing repetitions, for example 50,000 apples in your array might all weigh 3 ounces... You might therefore opt to implement a bucket sort to improve performance over a quicksort, which can be wasteful under such conditions. Here is an example implementation.

Perhaps benchmark a few researched choices, using the Java API when it suits, to determine the best solution for your input set.

回答2:

I would first use Java API. If this is not fast enough then I would search for a optimized sorting library.

Also consider a database, DB engines are fast and optimized for sorting large data sets.

回答3:

You can use Arrays.sort passing a custom Comparator or defining your Apple as Comparable

回答4:

We can use Collections.sort with a custom Comparator.

class Apple {
    public final int weight;
    // ...
};

List<Apple> apples = // ...

Collections.sort(apples, new Comparator<Apple>() {
    @Override public int compare(Apple a1, Apple a2) {
        return a1.weight - a2.weight; // Ascending
    }

});

回答5:

If in your object there is any Number or Integer over which you have to sort you can do like this-

List<Object> obj = new ArrayList<Object>();

Collections.sort(obj, new Comparator<Object>() {
    @Override
    public int compare(Object object1, Object object2) {
        return object1.getNumber() > object2.getNumber() ? 1 : -1;
    }
});

And if there is not Number or Integer over which you can sort it and you are just having Strings in your object than assign value to Strings by enum.

enum Code {
    Str1(1), Str2(2), Str3(3), Str4(4), Str5(5));

    int sortNumber;

    Code(int sortNumber) {
        this.sortNumber = sortNumber;
    }

    int returnNumber() {
        return sortNumber;
    }
};

public static void main(String[] args) {
    List<Object> obj = new ArrayList<Object>();

    Collections.sort(obj, new Comparator<Object>() {
        @Override
        public int compare(Object object1, Object object2) {
            return Code.valueOf(object1.getStr()).returnNumber() > Code.valueOf(object2.getStr()).returnNumber() ? 1 : -1;
        }
    });
}

来源：https://stackoverflow.com/questions/29777696/fastest-way-to-sort-an-array-of-objects-in-java

标签

java

arrays

sorting