Shulou(Shulou.com)06/03 Report--

In this issue, the editor will bring you about how to optimize the Javafor cycle Map collection. The article is rich in content and analyzes and describes for you from a professional point of view. I hope you can get something after reading this article.

On the basis of nested loops optimizing small loops to drive large loops, we optimize nested for loops with the efficient query performance of Map sets.

If the number of set elements of the small loop and the large loop is M and N respectively, the number of cycles of the double-layer For cycle is M-N, which has a greater and greater impact on the performance with the growth of M and N. Therefore, this paper considers further optimization to make the number of cycles become MIMO. Use the following code to simulate and test the performance of two situations:

Import java.util.ArrayList;import java.util.List;import java.util.Map;import java.util.function.Function;import java.util.stream.Collectors;public class ForUpdate {public static void main (String [] args) {/ / for (int I = 0; I)

< 10000; i += 10) {// loopGivenNum(i);// } for (int i = 10000; i < 100000; i += 10000) { loopGivenNum(i); } System.out.println("----- done -----"); } private static void loopGivenNum(int i) { List smallLoop = getLoopList(i); List bigLoop = getLoopList(2 * i); long doByForTimes = doByFor(bigLoop, smallLoop); long doByMapTimes = doByMap(bigLoop, smallLoop); System.out.println("size " + i + ": " + doByForTimes + "," + doByMapTimes); } /** * 获取循环变量 * @param size 循环变量元素个数 */ private static List getLoopList(int size) { List list = new ArrayList(); for (int i = 0; i < size; i++) { list.add(String.valueOf(i)); } return list; } private static long doByFor(List bigLoop, List smallLoop) { long startTime = System.currentTimeMillis(); for (String str1 : smallLoop) { for (String str2 : bigLoop) { if (str1.equals(str2)) { continue; } } } return System.currentTimeMillis() - startTime; } /** * 使用 Map 优化 * @param bigLoop * @param smallLoop */ private static long doByMap(List bigLoop, List smallLoop) { long startTime = System.currentTimeMillis(); // 转换成map Map loopMap = bigLoop.stream().collect(Collectors.toMap(k ->

K, Function.identity ()); System.out.println (loopMap.size ()); for (String str1: smallLoop) {if (loopMap.containsKey (str1)) {continue;}} return System.currentTimeMillis ()-startTime;}}

Output result:

Size 10000: 756,97size 20000: 3091,8size 30000: 4342,7size 40000: 8848,7size 50000: 16317,7size 60000: 31652,7size 70000: 37078,7

Thus it can be seen that the larger the amount of data, the longer the execution time of the nested For loop, and after using Map, even if the amount of data increases to 20w, the execution time is maintained at about 7ms. When the amount of data is small, the execution results will no longer be posted.

Conclusion: the efficiency of execution using Map optimized method is much higher than that of nested loops.

The above is the editor for you to share how to optimize the Javafor loop Map set to achieve, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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