看起来几乎没有任何区别。我为此创建了一个测试类。在五次运行的过程中,我的输出如下:
Run 1:
Arrays.asList() method................: 3231 ms
Arrays.stream() method................: 3111 ms
Stream.of() method....................: 3031 ms
Arrays.asList() (premade array) method: 3086 ms
Arrays.stream() (premade array) method: 3231 ms
Stream.of() (premade array) method....: 3191 ms
Run 2:
Arrays.asList() method................: 3270 ms
Arrays.stream() method................: 3072 ms
Stream.of() method....................: 3086 ms
Arrays.asList() (premade array) method: 3002 ms
Arrays.stream() (premade array) method: 3251 ms
Stream.of() (premade array) method....: 3271 ms
Run 3:
Arrays.asList() method................: 3307 ms
Arrays.stream() method................: 3092 ms
Stream.of() method....................: 2911 ms
Arrays.asList() (premade array) method: 3035 ms
Arrays.stream() (premade array) method: 3241 ms
Stream.of() (premade array) method....: 3241 ms
Run 4:
Arrays.asList() method................: 3630 ms
Arrays.stream() method................: 2981 ms
Stream.of() method....................: 2821 ms
Arrays.asList() (premade array) method: 3058 ms
Arrays.stream() (premade array) method: 3221 ms
Stream.of() (premade array) method....: 3214 ms
Run 5:
Arrays.asList() method................: 3338 ms
Arrays.stream() method................: 3174 ms
Stream.of() method....................: 3262 ms
Arrays.asList() (premade array) method: 3064 ms
Arrays.stream() (premade array) method: 3269 ms
Stream.of() (premade array) method....: 3275 ms
从输出结果来看,Stream.of()
方法似乎微不足道地(但一致地)最有效率,而
Stream.of("hallo","hi").forEach(System.out::println);
代码很易读。Stream.of的优点在于它不需要将数组转换为列表,也不需要创建数组然后创建流,而是可以直接从元素中创建流。对我来说有些惊讶的是,由于我的测试方式,每次使用Stream.of()
实例化一个新数组流要比传入预先制作的数组更快,可能是因为引用外部变量的“捕获”Lambda函数的效率稍低。
以下是我的测试类代码:
import java.util.Arrays;
import java.util.function.Consumer;
import java.util.stream.Stream;
public class StreamArrayTest {
public static void main(String[] args){
System.out.println("Arrays.asList() method................: " + arraysAsListMethod() + " ms");
System.out.println("Arrays.stream() method................: " + arraysStreamMethod() + " ms");
System.out.println("Stream.of() method....................: " + streamOfMethod() + " ms");
System.out.println("Arrays.asList() (premade array) method: " + presetArraysAsListMethod() + " ms");
System.out.println("Arrays.stream() (premade array) method: " + presetArraysStreamMethod() + " ms");
System.out.println("Stream.of() (premade array) method....: " + presetStreamsOfMethod() + " ms");
}
private static Long timeOneMillion(Runnable runner){
MilliTimer mt = MilliTimer.start();
for (int i = 0; i < 1000000; i++){
runner.run();
}
return mt.end();
}
private static Long timeOneMillion(String[] strings, Consumer<String[]> consumer){
MilliTimer mt = MilliTimer.start();
for (int i = 0; i < 1000000; i++){
consumer.accept(strings);
}
return mt.end();
}
public static Long arraysAsListMethod(){
return timeOneMillion(()->Arrays.asList(new String[]{"hallo","hi","test","test2","test3","test4","test5","test6","test7","test8"}).forEach(StreamArrayTest::doSomething));
}
public static Long arraysStreamMethod(){
return timeOneMillion(()->Arrays.stream(new String[]{"hallo","hi","test","test2","test3","test4","test5","test6","test7","test8"}).forEach(StreamArrayTest::doSomething));
}
public static Long streamOfMethod(){
return timeOneMillion(()->Stream.of("hallo","hi","test","test2","test3","test4","test5","test6","test7","test8").forEach(StreamArrayTest::doSomething));
}
public static Long presetArraysAsListMethod(){
String[] strings = new String[]{"hallo","hi","test","test2","test3","test4","test5","test6","test7","test8"};
return timeOneMillion(strings, (s)->Arrays.asList(s).forEach(StreamArrayTest::doSomething));
}
public static Long presetArraysStreamMethod(){
String[] strings = new String[]{"hallo","hi","test","test2","test3","test4","test5","test6","test7","test8"};
return timeOneMillion(strings, (s)->Arrays.stream(s).forEach(StreamArrayTest::doSomething));
}
public static Long presetStreamsOfMethod(){
String[] strings = new String[]{"hallo","hi","test","test2","test3","test4","test5","test6","test7","test8"};
return timeOneMillion(strings, (s)->Stream.of(s).forEach(StreamArrayTest::doSomething));
}
public static void doSomething(String s){
String result = s;
for (int i = 0; i < 10; i++){
result = result.concat(s);
}
}
}
我使用的MilliTimer类:
public class MilliTimer {
private long startTime = 0L;
private MilliTimer(long startTime){
this.startTime = startTime;
}
public static MilliTimer start(){
return new MilliTimer(System.currentTimeMillis());
}
public long end() throws IllegalArgumentException {
return System.currentTimeMillis() - startTime;
}
}
asList
,它涉及的对象较少。但在程序执行中仍然不会注意到任何差异。 - Sotirios Delimanolis"hello"
和"hi"
两个元素的列表,可以使用Arrays.asList("hello","hi")
方法来实现。这样做不需要先创建一个数组。 - Dici