使用Comparator接口与Lambda表达式排序int数组遇编译错误求助

Hey, let's break down what's going on here and fix your code!

The core issue you're hitting is that the Arrays.sort overload that takes a Comparator only works with object arrays (like Integer[]), not primitive type arrays (like int[]). The compiler error spells this out clearly when it mentions equality constraints: int and upper bounds: Object — since Comparator operates on types that inherit from Object, the primitive int can't be used with this method.

Solution 1: Use Integer[] with Lambda + Comparator #

If you specifically want to use a Lambda expression to define sorting logic, convert your primitive int[] to an Integer[] (boxed object array) first, sort it, then convert back if you need the primitive type:

import java.util.Arrays;

public class MyClass{
    public static void main(String args[]) {
        int[] arr = {5,3,7,8,1,4,6,9};
        
        // Convert primitive int array to Integer object array
        Integer[] integerArr = Arrays.stream(arr).boxed().toArray(Integer[]::new);
        
        // Sort using Lambda as Comparator (ascending order here)
        Arrays.sort(integerArr, (o1, o2) -> o1 - o2);
        
        // Convert back to int array if needed
        int[] sortedArr = Arrays.stream(integerArr).mapToInt(Integer::intValue).toArray();
        
        System.out.println(Arrays.toString(sortedArr));
    }
}

Solution 2: Use the default Arrays.sort(int[]) for simple ascending sort #

If you just need a standard ascending sort, you don't need a Comparator at all! The default Arrays.sort(int[]) method is built specifically for primitive integer arrays and does exactly what you want:

import java.util.Arrays;
public class MyClass{
    public static void main(String args[]) {
        int[] arr = {5,3,7,8,1,4,6,9};
        Arrays.sort(arr); // Default ascending sort for primitive int array
        System.out.println(Arrays.toString(arr));
    }
}

Bonus: Custom sort (e.g., descending order) for primitive arrays #

If you need a custom order like descending, you can use streams to handle boxing and sorting in one chain:

import java.util.Arrays;
public class MyClass{
    public static void main(String args[]) {
        int[] arr = {5,3,7,8,1,4,6,9};
        
        int[] sortedDescArr = Arrays.stream(arr)
                                    .boxed()
                                    .sorted((o1, o2) -> o2 - o1) // Descending order
                                    .mapToInt(Integer::intValue)
                                    .toArray();
                                    
        System.out.println(Arrays.toString(sortedDescArr));
    }
}

内容的提问来源于stack exchange，提问作者Harsh Shah