[英]Inline comparator vs custom comparator in Java
排序列表时,使用java Comparator内联(使用匿名内部类)与实现单独的自定义Comparator类之间是否有任何性能差异?
1。
public class SortByErrorComparator implements Comparator<WorkflowError> {
public int compare(WorkflowError obj1, WorkflowError obj2) {
return obj1.getErrorCode().compareTo(obj2.getErrorCode());
}
}
Collections.sort(list, new SortByErrorComparator()) ;
2。
Collections.sort(list, new Comparator<WorkflowError>() {
public int compare(WorkflowError obj1, WorkflowError obj2) {
return obj1.getErrorCode().compareTo(obj2.getErrorCode());
}
});
此外,何时调用compare()
方法?
这两个变体之间不应该有任何性能差异,因为匿名类应该生成与常规类相同的字节代码(假设它们具有相同的源代码)。 唯一的区别是他们将生成一个名称。
只要需要比较要排序的List的两个元素, Collections.sort
就会调用compare
方法。
我做了一个小测试,发现没有区别(只是在一些小的运行中,内联比较器显示稍微更好的性能)。 这是用于进行测试的代码:
public class ComparatorTest {
private static final int MAX = 1000000;
private static final int RUN = 10000;
public static void main(String[] args) {
List<A> list = new ArrayList<A>();
long externalComparatorClassTotalTime = 0;
long inlineCompartorTotalTime = 0;
for (int i = RUN; i > 0; i--) {
init(list);
externalComparatorClassTotalTime += externalComparatorClassTest(list);
init(list);
inlineCompartorTotalTime += inlineCompartorTest(list);
}
System.out.format("List with %d elements and %d runs%n", MAX, RUN);
System.out.println("external Comparator class average millis: " + externalComparatorClassTotalTime / RUN);
System.out.println("inline Comparator class average millis: " + inlineCompartorTotalTime / RUN);
}
private static void init(List<A> list) {
list.clear();
for (int i = MAX; i > 0; i--) {
list.add(new A(i));
}
}
private static long inlineCompartorTest(List<A> secondList) {
long start = System.currentTimeMillis();
Collections.sort(secondList, new Comparator<A>() {
public int compare(A obj1, A obj2) {
return obj1.getVal().compareTo(obj2.getVal());
}
});
return System.currentTimeMillis() - start;
}
private static long externalComparatorClassTest(List<A> firstList) {
long start = System.currentTimeMillis();
Collections.sort(firstList, new MyComparatorOne());
return System.currentTimeMillis() - start;
}
}
比较类:
public class MyComparatorOne implements Comparator<A> {
public int compare(A obj1, A obj2) {
return obj1.getVal().compareTo(obj2.getVal());
}
}
输出是:
List with 1000000 elements and 10000 runs
external Comparator class average millis: 3
inline Comparator class average millis: 3
如果您有几次调用比较器,保持它的实例将是有帮助的
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