# 測試代碼LamdaTest.java
import java.util.*;class LamdaTest {static volatile List<Integer> integers = new ArrayList<Integer>();// 普通 for 循環測試public static int forLoopInteger() {int total = 0;for (int i = 0; i < integers.size(); i++) {total += integers.get(i);}System.out.println("total: " + total);return total;}// forEach 循環測試public static int forOfInteger() {int total = 0;for (Integer n : integers) {total += n;}System.out.println("total: " + total);return total;}// lamda map循環測試public static int lambdaInteger() {int total = 0;integers.forEach(n -> {// System.out.println("n:" + n);});// total = integers.stream().reduce(0, (a, b) -> {// return a + b;// });System.out.println("total: " + total);return total;}public static void main(String[] args) {// 初始化integers，填充內容for (int i = 0; i < 100000; i++) {integers.add(i);}long startTime = 0L;long costTime = 0L;System.out.println("forLoopInteger start: ");startTime = System.currentTimeMillis();forLoopInteger();costTime = System.currentTimeMillis() - startTime;System.out.println("forLoopInteger cost: " + costTime);System.out.println("====");startTime = System.currentTimeMillis();System.out.println("forOfInteger start: ");forOfInteger();costTime = System.currentTimeMillis() - startTime;System.out.println("forOfInteger cost: " + costTime);System.out.println("====");startTime = System.currentTimeMillis();System.out.println("lambdaInteger start: ");lambdaInteger();costTime = System.currentTimeMillis() - startTime;System.out.println("lambdaInteger cost: " + costTime);}
}/*** // 測試1結果* java -version* java version "1.8.0_401"* Java(TM) SE Runtime Environment (build 1.8.0_401-b10)* Java HotSpot(TM) 64-Bit Server VM (build 25.401-b10, mixed mode)* * 第一組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 6* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 7* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 50* * 第二組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 5* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 5* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 46* * 第三組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 5* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 7* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 47*//*** // 測試2結果* java -version* openjdk version "11.0.4" 2019-07-16 LTS* OpenJDK Runtime Environment 18.9 (build 11.0.4+11-LTS)* OpenJDK 64-Bit Server VM 18.9 (build 11.0.4+11-LTS, mixed mode, sharing)* * 第一組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 115* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 40* ====* lambdaInteger start:* total: 704982704* lambdaInteger cost: 166* * 第二組：* forLoopMaxInteger start:* total: 704982704* forLoopMaxInteger cost: 55* ====* forOfMaxInteger start:* total: 704982704* forOfMaxInteger cost: 27* ====* lambdaMaxInteger start:* total: 704982704* lambdaMaxInteger cost: 31* * 第三組：* forLoopMaxInteger start:* total: 704982704* forLoopMaxInteger cost: 51* ====* forOfMaxInteger start:* total: 704982704* forOfMaxInteger cost: 29* ====* lambdaMaxInteger start:* total: 704982704* lambdaMaxInteger cost: 29*//*** // 測試3結果* java -version* java version "10.0.1" 2018-04-17* Java(TM) SE Runtime Environment 18.3 (build 10.0.1+10)* Java HotSpot(TM) 64-Bit Server VM 18.3 (build 10.0.1+10, mixed mode)* * 第一組：* java LamdaTest* forLoopInteger start:* total: 704982704* forLoopInteger cost: 33* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 6* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 7* * 第二組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 33* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 6* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 8* * 第三組：* forLoopInteger start:* total: 704982704* forLoopInteger cost: 35* ====* forOfInteger start:* total: 704982704* forOfInteger cost: 8* ====* lambdaInteger start:* total: 0* lambdaInteger cost: 9*/結論
通過以上測試，JDK1.8下lambda確實有性能問題，但之后版本lambda做了性能優化，不會有性能問題了，甚至更快。
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