我在这里有一个案例，其中 switch 语句包含大约 40 个案例，每个案例都根据输入返回不同的配置对象。这种方法在度量中显示为具有太高的圈复杂度，通常我会将其更改为处理程序对象的映射。但是这个开关位于一段代码中，其中性能是最重要的，所以我想出了一个问题，即 HashMap 查找和处理程序调用如何与开关块执行性能进行比较。有人比较过吗？值得考虑吗？或者对于有限数量的 int 键是否有更快的查找对象？
干杯，凯
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我很确定 a 的内部表示switch使用某种与 a 具有相似结构的查找表HashMap，所以我的猜测是任何差异都可以忽略不计。
我会说性能在这里不值得考虑，只要使用为您提供最干净代码的任何解决方案即可。
于 2013-04-23T19:44:22.050 回答
0
似乎搜索值比切换方法略快。因此，如果您的代码更改经常集中在哈希方法上，如果它经过优化并且不会经常更改，您可以使用 switch 方法而不会后悔。如果您的应用程序正在由多个程序员开发，您应该更喜欢散列方法以防止将来出现错误。
开关版本：27.32191395 ns。哈希版本：26.98444367 ns。
使用哈希获得的时间：1.23%。
我使用以下代码对其进行了测试：
导入 java.util.Random；
/**
* @author ruslan.lopez
*/
public class CyclomaticVsHash {
private static final Random RNG = new Random();
static int[] myHash = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 };
/**
* @param args
* the command line arguments
*/
public static void main(String[] args) {
long iterations = 100000000;
warmUp(iterations);
System.out.println("Cycle1");
double individualTime = getAverageTimePerIterationc1(iterations);
iterations = 10000;
double totalTime = getTotalTimec1(iterations);
System.out.println("ns/iteration: " + individualTime);
System.out.println("Total time for " + iterations + " runs: "
+ totalTime);
System.out.println("Cycle2");
iterations = 100000000;
warmUp(iterations);
double individualTime1 = getAverageTimePerIterationc2(iterations);
iterations = 10000;
double totalTime1 = getTotalTimec2(iterations);
System.out.println("ns/iteration: " + individualTime1);
System.out.println("Total time for " + iterations + " runs: "
+ totalTime1);
}
public static void warmUp(long iterations) {
System.out.println("Starting warmup");
for (int i = 0; i < iterations; i++) {
runCycles();
runCycles1();
}
}
public static double getAverageTimePerIterationc1(long iterations) {
// test
System.out.println("Starting individual time test");
long timeTaken = 0;
for (int i = 0; i < iterations; i++) {
long startTime = System.nanoTime();
runCycles();
timeTaken += System.nanoTime() - startTime;
}
return (double) timeTaken / iterations;
}
public static long getTotalTimec1(long iterations) {
// test
System.out.println("Starting total time test");
long timeTaken = 0;
for (int i = 0; i < iterations; i++) {
long startTime = System.nanoTime();
runCycles();
timeTaken += System.nanoTime() - startTime;
}
return timeTaken;
}
public static double getAverageTimePerIterationc2(long iterations) {
// test
System.out.println("Starting individual time test");
long timeTaken = 0;
for (int i = 0; i < iterations; i++) {
long startTime = System.nanoTime();
runCycles1();
timeTaken += System.nanoTime() - startTime;
}
return (double) timeTaken / iterations;
}
public static long getTotalTimec2(long iterations) {
// test
System.out.println("Starting total time test");
long timeTaken = 0;
for (int i = 0; i < iterations; i++) {
long startTime = System.nanoTime();
runCycles1();
timeTaken += System.nanoTime() - startTime;
}
return timeTaken;
}
private static void runCycles() {
Integer num = RNG.nextInt();
int newnum;
switch (num) {
case 1:
newnum = num * 1;
break;
case 2:
newnum = num * 2;
break;
case 3:
newnum = num * 3;
break;
case 4:
newnum = num * 4;
break;
case 5:
newnum = num * 5;
break;
case 6:
newnum = num * 6;
break;
case 7:
newnum = num * 7;
break;
case 8:
newnum = num * 8;
break;
case 9:
newnum = num * 9;
break;
case 10:
newnum = num * 10;
break;
case 11:
newnum = num * 11;
break;
case 12:
newnum = num * 12;
break;
case 13:
newnum = num * 13;
break;
case 14:
newnum = num * 14;
break;
case 15:
newnum = num * 15;
break;
case 16:
newnum = num * 16;
break;
case 17:
newnum = num * 17;
break;
case 18:
newnum = num * 18;
break;
case 19:
newnum = num * 19;
break;
case 20:
newnum = num * 20;
break;
case 21:
newnum = num * 21;
break;
case 22:
newnum = num * 22;
break;
case 23:
newnum = num * 23;
break;
case 24:
newnum = num * 24;
break;
case 25:
newnum = num * 25;
break;
case 26:
newnum = num * 26;
break;
case 27:
newnum = num * 7;
break;
case 28:
newnum = num * 28;
break;
case 29:
newnum = num * 29;
break;
case 30:
newnum = num * 30;
break;
case 31:
newnum = num * 31;
break;
case 32:
newnum = num * 32;
break;
case 33:
newnum = num * 33;
break;
case 34:
newnum = num * 34;
break;
case 35:
newnum = num * 35;
break;
case 36:
newnum = num * 36;
break;
case 37:
newnum = num * 37;
break;
case 38:
newnum = num * 38;
break;
case 39:
newnum = num * 39;
break;
default:
newnum = num * 40;
break;
}
}
private static void runCycles1() {
Integer num = RNG.nextInt();
int nwenum = num > 0 && num < 39
? myHash[num - 1]
: myHash[39];
}
}
于 2015-11-17T16:10:01.387 回答