[英]Inline comparator vs custom comparator in Java
排序列表時,使用java Comparator內聯(使用匿名內部類)與實現單獨的自定義Comparator類之間是否有任何性能差異?
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,何時調用compare()
方法?
這兩個變體之間不應該有任何性能差異,因為匿名類應該生成與常規類相同的字節代碼(假設它們具有相同的源代碼)。 唯一的區別是他們將生成一個名稱。
只要需要比較要排序的List的兩個元素, Collections.sort
就會調用compare
方法。
我做了一個小測試,發現沒有區別(只是在一些小的運行中,內聯比較器顯示稍微更好的性能)。 這是用於進行測試的代碼:
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;
}
}
比較類:
public class MyComparatorOne implements Comparator<A> {
public int compare(A obj1, A obj2) {
return obj1.getVal().compareTo(obj2.getVal());
}
}
輸出是:
List with 1000000 elements and 10000 runs
external Comparator class average millis: 3
inline Comparator class average millis: 3
如果您有幾次調用比較器,保持它的實例將是有幫助的
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