英文:
Java int[] comparator
问题
尝试为int[]编写自定义比较器，代码如下所示：
public class ArrayComparator implements Comparator<int[]>{
@Override
public int compare(int[] a, int[] b){
return a[1] - b[1];
}
}
但是在a = [-2147483646,-2147483645],[2147483646,2147483647]，b = [-2147483646,-2147483645],[2147483646,2147483647]这种情况下是不正确的。我应该如何修改我的代码？
英文:
Trying to write a custom comparator for int[] as follows:
public class arrayComparator implements Comparator<int[]>{
@Override
public int compare(int[] a, int[] b){
return a[1] - b[1];
}
}
But this is not correct for the case where a = [-2147483646,-2147483645],[2147483646,2147483647], b = [-2147483646,-2147483645],[2147483646,2147483647]. How should I revise my code?
答案1
得分: 7
为了避免在比较int值时出现整数溢出问题，我们应该始终使用内置的Integer.compare(int,int)来比较自然顺序。
所以将代码中的：
return a[1] - b[1];
改为：
return Integer.compare(a[1], b[1]);
另外，由于Comparator是一个函数式接口，我们可以通过lambda表达式和/或方法引用来提供其实现：
Comparator<int[]> arrayComparator1 = (a, b) -> Integer.compare(a[1], b[1]);
Comparator<int[]> arrayComparator2 = Comparator.comparingInt(arr -> arr[1]);
除了主要问题之外，Java的普遍接受的编码风格是非原始类型的名称应以大写字母开头，例如String、ArrayList。所以将arrayComparator改为ArrayComparator。
英文:
Precisely to avoid that kind of problems with integer overflow, to compare int values with natural order we should always use built-in Integer.compare(int,int).
So change
return a[1] - b[1];
into
return Integer.compare(a[1], b[1]);
BTW since Comparator is functional interface we can provide its implementation via lambdas and/or method-references:
Comparator<int[]> arrayComparator1 = (a, b) -> Integer.compare(a[1], b[1]);
Comparator<int[]> arrayComparator2 = Comparator.comparingInt(arr -> arr[1]);
Aside from main question, generally accepted coding style for Java is that names of non-primitive-types should start with uppercase like String ArrayList. So change arrayComparator into ArrayComparator.
答案2
得分: 1
以下是翻译好的部分：
public class arrayComparator implements Comparator<int[]> {
@Override
public int compare(int[] a, int[] b) {
return a[1] > b[1] ? 1 : a[1] < b[1] ? -1 : 0;
}
}
或
public class arrayComparator implements Comparator<int[]> {
@Override
public int compare(int[] a, int[] b) {
if (a[1] > b[1]) {
return 1;
}
if (a[1] < b[1]) {
return -1;
}
return 0;
}
}
或
public class arrayComparator implements Comparator<int[]> {
@Override
public int compare(int[] a, int[] b) {
return Integer.compare(a[1], b[1]);
}
}
英文:
Since you're learning about this, here are several ways of doing it.
public arrayComparator implements Comparator<int[]>{
@Override
public int compare(int[] a, int[] b){
return a[1] > b[1] ? 1 : a[1] < b[1] ? -1 : 0;
}
}
Or
public arrayComparator implements Comparator<int[]>{
@Override
public int compare(int[] a, int[] b){
if (a[1] > b[1]) {
return 1;
}
if (a[1] < b[1]) {
return -1;
}
return 0;
}
}
Or
public arrayComparator implements Comparator<int[]>{
@Override
public int compare(int[] a, int[] b){
return Integer.compare(a[1], b[1]);
}
}
</details>
# 答案3
**得分**: 0
更简单的写法：
```java
Comparator<int[]> intArrayComparator = (a, b) -> Integer.compare(a[1], b[1]);
例如，可以这样使用：
int[][] arr = ....;
Arrays.sort(arr, intArrayComparator);
无需为此创建显式命名的自定义类。
英文:
Even simpler:
Comparator<int[]> intArrayComparator = (a, b) -> Integer.compare(a[1], b[1]);
For example, to be used as:
int[][] arr = ....;
Arrays.sort(arr, intArrayComparator);
There's no need to make an explicitly named custom class for this.
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