我编写了三种方法来使用for循环，Stream s（Java 8）和并行Stream（Java 8）获取目录中的文件/文件夹列表。我看到for循环比Java 8 Stream快得多。我的印象是Java 8的Stream是一种改进？
请参阅下面的方法：
private static List<String> getListOfFiles() throws Exception {
long startTime = System.nanoTime();
List<String> xmlFileList = new ArrayList<String>();
File[] workspaceFiles = new File(USER_FOLDER).listFiles();
try {
for (File file : workspaceFiles) {
if (!file.toString().contains(FOLDER)) {
xmlFileList.add(file.getAbsolutePath());
}
}
} catch (Exception e) {
e.printStackTrace();
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
System.out.println("Regular For Loop : " + duration);
return xmlFileList;
}
private static List<String> getListOfFilesStream() throws IOException {
long startTime = System.nanoTime();
List<String> listOfFiles = new ArrayList<String>();
try (Stream<Path> stream = Files.list(Paths.get(USER_FOLDER))) {
listOfFiles = stream.filter(file -> !file.getFileName().toString().contains(FOLDER))
.map(filePath -> filePath.toString()).collect(Collectors.toList());
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
System.out.println("Stream : " + duration);
return listOfFiles;
}
private static List<String> getListOfFilesParallel() throws IOException {
long startTime = System.nanoTime();
List<String> listOfFiles = new ArrayList<String>();
try (Stream<Path> stream = Files.list(Paths.get(USER_FOLDER))) {
listOfFiles = stream.parallel()
.filter(file -> !file.getFileName().toString().contains(FOLDER))
.map(filePath -> filePath.toString()).collect(Collectors.toList());
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
System.out.println("Parallel Stream : " + duration);
return listOfFiles;
}
输出结果为：
Regular For Loop : 406743
Stream : 54629961
Parallel Stream : 3791280
使用-XX:+PrintCompilation, -verbose:gc
for循环结果：
50 1 3 java.lang.String::hashCode (55 bytes)
51 2 3 java.lang.String::charAt (29 bytes)
51 4 n 0 java.lang.System::arraycopy (native) (static)
51 3 3 java.lang.Object::<init> (1 bytes)
51 5 3 java.lang.String::<init> (82 bytes)
52 7 3 java.lang.String::equals (81 bytes)
52 6 3 java.util.Arrays::copyOfRange (63 bytes)
52 8 3 java.lang.Math::min (11 bytes)
53 9 3 java.lang.AbstractStringBuilder::ensureCapacityInternal (16 bytes)
53 10 3 java.lang.String::indexOf (70 bytes)
54 11 3 java.lang.String::length (6 bytes)
54 12 1 java.lang.ref.Reference::get (5 bytes)
54 13 3 java.lang.String::getChars (62 bytes)
55 14 3 java.lang.String::indexOf (7 bytes)
55 15 1 java.lang.ThreadLocal::access$400 (5 bytes)
60 16 3 java.lang.AbstractStringBuilder::append (50 bytes)
62 17 3 java.lang.System::getSecurityManager (4 bytes)
62 18 3 java.lang.StringBuilder::append (8 bytes)
62 20 3 java.lang.AbstractStringBuilder::expandCapacity (50 bytes)
63 19 3 java.util.Arrays::copyOf (19 bytes)
Regular For Loop : 418313
63 21 1 java.io.File::getPath (5 bytes)
Stream结果：
49 1 3 java.lang.String::hashCode (55 bytes)
50 2 3 java.lang.String::charAt (29 bytes)
50 4 n 0 java.lang.System::arraycopy (native) (static)
50 3 3 java.lang.Object::<init> (1 bytes)
50 5 3 java.lang.String::<init> (82 bytes)
51 7 3 java.lang.String::equals (81 bytes)
51 6 3 java.util.Arrays::copyOfRange (63 bytes)
52 8 3 java.lang.Math::min (11 bytes)
53 10 3 java.lang.String::indexOf (70 bytes)
53 11 3 java.lang.String::length (6 bytes)
53 9 3 java.lang.AbstractStringBuilder::ensureCapacityInternal (16 bytes)
53 12 1 java.lang.ref.Reference::get (5 bytes)
53 13 3 java.lang.String::getChars (62 bytes)
55 14 3 java.lang.String::indexOf (7 bytes)
55 15 1 java.lang.ThreadLocal::access$400 (5 bytes)
59 16 3 java.lang.AbstractStringBuilder::append (50 bytes)
62 17 3 java.lang.System::getSecurityManager (4 bytes)
70 18 3 java.lang.Number::<init> (5 bytes)
70 19 3 java.lang.Byte::<init> (10 bytes)
71 20 3 java.lang.Short::<init> (10 bytes)
71 21 3 java.lang.Long::<init> (10 bytes)
72 22 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLL)L (native) (static)
73 23 3 java.lang.StringBuilder::append (8 bytes)
74 25 n 0 sun.misc.Unsafe::getObjectVolatile (native)
74 24 3 java.util.concurrent.ConcurrentHashMap::tabAt (21 bytes)
74 26 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLL)L (native) (static)
75 27 1 java.lang.reflect.Method::getName (5 bytes)
75 28 n 0 java.lang.invoke.MethodHandle::linkToStatic(LL)L (native) (static)
75 29 1 java.lang.Class::getClassLoader0 (5 bytes)
75 30 n 0 java.lang.Object::hashCode (native)
75 31 1 java.lang.Enum::ordinal (5 bytes)
76 32 4 java.lang.String::charAt (29 bytes)
77 2 3 java.lang.String::charAt (29 bytes) made not entrant
78 33 n 0 java.lang.invoke.MethodHandle::linkToStatic(LL)V (native) (static)
78 34 1 java.lang.Object::<init> (1 bytes)
78 3 3 java.lang.Object::<init> (1 bytes) made not entrant
78 35 3 java.lang.String::lastIndexOf (52 bytes)
78 36 n 0 java.lang.invoke.MethodHandle::linkToStatic(LL)J (native) (static)
79 38 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLL)L (native) (static)
79 37 3 java.lang.ref.Reference::<init> (25 bytes)
79 39 3 java.util.Arrays::copyOf (19 bytes)
79 40 3 java.lang.invoke.MemberName::testFlags (16 bytes)
79 41 3 java.lang.AbstractStringBuilder::append (29 bytes)
80 42 3 java.lang.Class::getName (21 bytes)
80 43 n 0 java.lang.Class::isPrimitive (native)
80 44 1 java.lang.invoke.MethodType::returnType (5 bytes)
80 45 3 java.lang.Class::getClassLoader (28 bytes)
80 46 1 java.lang.invoke.MemberName::getDeclaringClass (5 bytes)
81 47 3 java.lang.StringBuilder::append (8 bytes)
81 48 3 jdk.internal.org.objectweb.asm.ByteVector::putUTF8 (142 bytes)
81 49 3 jdk.internal.org.objectweb.asm.Item::set (143 bytes)
82 50 3 jdk.internal.org.objectweb.asm.ByteVector::putShort (52 bytes)
82 51 3 jdk.internal.org.objectweb.asm.ClassWriter::get (49 bytes)
82 53 3 java.lang.AbstractStringBuilder::expandCapacity (50 bytes)
83 52 3 jdk.internal.org.objectweb.asm.ByteVector::putByte (39 bytes)
83 54 1 java.lang.invoke.MethodType$ConcurrentWeakInternSet$WeakEntry::hashCode (5 bytes)
83 55 1 java.util.SubList::access$000 (5 bytes)
83 56 1 java.util.AbstractList$ListItr::nextIndex (5 bytes)
84 57 1 java.util.SubList::access$200 (5 bytes)
84 58 3 java.util.concurrent.ConcurrentHashMap::spread (10 bytes)
84 59 1 java.lang.String::length (6 bytes)
84 11 3 java.lang.String::length (6 bytes) made not entrant
84 60 3 java.util.Objects::requireNonNull (14 bytes)
84 61 3 java.lang.invoke.MemberName::isInvocable (7 bytes)
84 62 n 0 java.lang.Object::getClass (native)
85 64 3 java.lang.String::replace (127 bytes)
85 63 1 java.util.ArrayList::access$100 (5 bytes)
85 65 3 java.lang.String::lastIndexOf (13 bytes)
85 66 1 java.util.ArrayList::size (5 bytes)
85 67 ! 3 java.util.concurrent.ConcurrentHashMap::putVal (362 bytes)
86 71 n 0 java.lang.invoke.MethodHandle::linkToVirtual(LL)L (native) (static)
87 69 3 jdk.internal.org.objectweb.asm.Item::<init> (66 bytes)
87 72 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLL)V (native) (static)
87 70 3 jdk.internal.org.objectweb.asm.ClassWriter::put (152 bytes)
87 73 n 0 java.lang.Class::isArray (native)
87 75 n 0 java.lang.invoke.MethodHandle::invokeBasic(L)L (native)
87 68 ! 3 java.lang.ref.ReferenceQueue::poll (28 bytes)
87 76 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLL)L (native) (static)
87 74 3 java.lang.reflect.Modifier::isStatic (13 bytes)
87 77 3 jdk.internal.org.objectweb.asm.ClassWriter::newUTF8 (70 bytes)
88 78 3 java.lang.invoke.MethodType::checkSlotCount (33 bytes)
88 80 n 0 java.lang.Object::clone (native)
88 79 3 java.lang.invoke.MemberName::testAllFlags (7 bytes)
88 81 n 0 java.lang.invoke.MethodHandle::linkToStatic(L)L (native) (static)
88 82 3 java.lang.String::indexOf (166 bytes)
88 84 n 0 java.lang.invoke.MethodHandle::invokeBasic()L (native)
89 86 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LL)L (native) (static)
89 83 3 java.lang.AbstractStringBuilder::<init> (12 bytes)
89 85 ! 3 java.lang.invoke.MemberName::getMethodType (208 bytes)
89 88 n 0 java.lang.invoke.MethodHandle::invokeBasic(LL)L (native)
89 89 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLL)L (native) (static)
90 87 1 java.lang.invoke.MethodType::form (5 bytes)
90 90 3 jdk.internal.org.objectweb.asm.ByteVector::put12 (64 bytes)
90 93 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLL)L (native)
90 94 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLL)L (native) (static)
90 95 3 java.lang.ref.Reference::<init> (7 bytes)
90 92 3 java.util.concurrent.ConcurrentHashMap::putIfAbsent (8 bytes)
90 91 1 java.lang.invoke.MethodType::ptypes (5 bytes)
90 96 1 java.lang.invoke.LambdaForm$Name::index (5 bytes)
90 97 1 sun.invoke.util.Wrapper::basicTypeChar (5 bytes)
90 98 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLL)L (native) (static)
91 99 3 java.lang.invoke.MemberName::isConstructor (7 bytes)
91 100 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLL)L (native)
91 101 3 java.lang.invoke.MemberName::getMethodOrFieldType (72 bytes)
91 103 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLL)L (native) (static)
91 106 4 java.lang.String::hashCode (55 bytes)
91 107 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLL)L (native) (static)
92 102 3 java.lang.ref.WeakReference::<init> (6 bytes)
92 104 3 java.lang.invoke.LambdaForm$BasicType::basicType (19 bytes)
92 112 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLL)L (native)
92 105 1 java.lang.invoke.LambdaForm$Name::type (5 bytes)
92 114 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLL)L (native) (static)
92 113 3 java.lang.Object::equals (11 bytes)
92 109 1 java.lang.invoke.LambdaForm$BasicType::basicTypeChar (5 bytes)
92 108 1 java.lang.invoke.LambdaForm$Name::access$000 (5 bytes)
92 110 1 java.lang.invoke.LambdaForm$BasicType::access$100 (5 bytes)
92 111 1 java.lang.invoke.LambdaForm$BasicType::basicTypeClass (5 bytes)
93 115 3 java.lang.invoke.MemberName::isStatic (8 bytes)
93 116 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLLL)L (native)
93 117 3 java.lang.invoke.MethodType::hashCode (53 bytes)
93 119 n 0 sun.misc.Unsafe::putObjectVolatile (native)
93 120 n 0 sun.misc.Unsafe::compareAndSwapObject (native)
93 121 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLLL)L (native) (static)
93 118 3 java.util.concurrent.ConcurrentHashMap::setTabAt (19 bytes)
93 1 3 java.lang.String::hashCode (55 bytes) made not entrant
93 122 3 java.lang.invoke.MethodType$ConcurrentWeakInternSet::expungeStaleElements (27 bytes)
93 123 ! 3 java.util.AbstractList$Itr::next (45 bytes)
93 125 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLL)L (native) (static)
93 126 3 java.lang.invoke.MethodType::parameterType (7 bytes)
94 127 3 java.lang.StringBuilder::toString (17 bytes)
94 124 3 java.util.AbstractList$Itr::checkForComodification (23 bytes)
94 129 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLLLL)L (native)
94 128 3 java.lang.invoke.LambdaForm::argument (27 bytes)
94 130 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLLLL)L (native) (static)
94 131 3 java.lang.invoke.MethodType::checkPtype (19 bytes)
94 132 n 0 java.lang.Class::isInterface (native)
94 133 3 java.util.Arrays$ArrayList::size (6 bytes)
94 134 3 java.util.Collections$UnmodifiableCollection$1::hasNext (10 bytes)
94 135 1 java.lang.invoke.MethodHandle::type (5 bytes)
94 136 3 java.lang.invoke.MethodTypeForm::canonicalize (233 bytes)
95 137 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLLL)L (native) (static)
95 140 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLLLLL)L (native)
95 141 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLLLLL)L (native) (static)
95 138 3 jdk.internal.org.objectweb.asm.Type::getArgumentsAndReturnSizes (151 bytes)
95 145 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLLLL)L (native) (static)
96 139 3 java.lang.invoke.InvokerBytecodeGenerator::isStaticallyNameable (116 bytes)
96 146 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLLLLLL)L (native)
96 147 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLLLLLL)L (native) (static)
96 150 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLLLLL)L (native) (static)
97 143 3 jdk.internal.org.objectweb.asm.Frame::execute (2252 bytes)
97 151 n 0 java.lang.invoke.MethodHandle::invokeBasic(LLLLLLLLLL)L (native)
97 153 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LLLLLLLLLLLL)L (native) (static)
98 154 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLLLLLL)L (native) (static)
99 156 n 0 java.lang.invoke.MethodHandle::linkToStatic(LLLLLLLLLLLLL)L (native) (static)
99 157 4 jdk.internal.org.objectweb.asm.ByteVector::putUTF8 (142 bytes)
100 158 n 0 java.lang.invoke.MethodHandle::linkToStatic(LIL)V (native) (static)
100 159 n 0 java.lang.invoke.MethodHandle::linkToStatic(ILL)I (native) (static)
101 152 3 java.util.concurrent.ConcurrentHashMap::get (162 bytes)
102 149 s 3 java.lang.StringBuffer::append (13 bytes)
102 144 3 jdk.internal.org.objectweb.asm.Item::isEqualTo (354 bytes)
103 148 3 java.lang.invoke.MethodType::makeImpl (66 bytes)
103 160 n 0 java.lang.invoke.MethodHandle::linkToStatic(ILLL)L (native) (static)
103 164 n 0 java.lang.invoke.MethodHandle::invokeBasic(ILL)L (native)
103 142 3 java.lang.String::substring (79 bytes)
103 165 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LILLL)L (native) (static)
103 161 3 java.lang.invoke.LambdaForm$Name::initIndex (26 bytes)
104 162 3 java.lang.invoke.LambdaForm$BasicType::basicTypeSlots (8 bytes)
104 168 3 java.util.Arrays$ArrayList::get (7 bytes)
104 163 3 sun.invoke.util.Wrapper::stackSlots (9 bytes)
104 166 3 jdk.internal.org.objectweb.asm.MethodWriter::visitVarInsn (292 bytes)
104 169 3 sun.invoke.util.VerifyAccess::isSamePackage (114 bytes)
105 48 3 jdk.internal.org.objectweb.asm.ByteVector::putUTF8 (142 bytes) made not entrant
105 175 3 jdk.internal.org.objectweb.asm.Type::getType (269 bytes)
106 170 3 jdk.internal.org.objectweb.asm.Frame::push (110 bytes)
106 174 3 java.lang.String::<init> (10 bytes)
106 173 3 jdk.internal.org.objectweb.asm.ClassWriter::addType (39 bytes)
106 176 3 java.lang.invoke.MethodType$ConcurrentWeakInternSet$WeakEntry::<init> (14 bytes)
106 172 3 java.lang.invoke.LambdaForm$BasicType::basicType (172 bytes)
107 167 3 java.lang.invoke.InvokerBytecodeGenerator::emitImplicitConversion (159 bytes)
108 180 3 java.lang.invoke.LambdaForm$NamedFunction::methodType (23 bytes)
108 181 3 jdk.internal.org.objectweb.asm.Frame::type (416 bytes)
108 182 4 java.lang.String::indexOf (70 bytes)
108 179 3 java.lang.StringBuilder::<init> (7 bytes)
109 178 3 java.lang.String::indexOf (25 bytes)
109 184 4 java.lang.String::equals (81 bytes)
109 177 3 java.lang.String::indexOf (7 bytes)
109 183 3 jdk.internal.org.objectweb.asm.Frame::get (46 bytes)
109 185 3 java.lang.invoke.InvokerBytecodeGenerator::emitLoadInsn (21 bytes)
109 186 3 java.lang.invoke.InvokerBytecodeGenerator::loadInsnOpcode (86 bytes)
109 10 3 java.lang.String::indexOf (70 bytes) made not entrant
110 189 3 java.util.AbstractList$Itr::hasNext (20 bytes)
110 187 s 3 java.lang.StringBuffer::append (15 bytes)
110 188 3 java.lang.AbstractStringBuilder::append (40 bytes)
110 171 1 java.lang.invoke.LambdaForm::arity (5 bytes)
110 155 1 java.lang.invoke.MethodTypeForm::erasedType (5 bytes)
111 190 3 java.util.AbstractCollection::<init> (5 bytes)
112 7 3 java.lang.String::equals (81 bytes) made not entrant
112 191 3 jdk.internal.org.objectweb.asm.ByteVector::<init> (13 bytes)
112 192 3 jdk.internal.org.objectweb.asm.ByteVector::putByteArray (49 bytes)
112 193 n 0 java.lang.invoke.MethodHandle::linkToStatic(LL)I (native) (static)
112 194 3 java.lang.invoke.MethodType$ConcurrentWeakInternSet::get (54 bytes)
113 195 3 jdk.internal.org.objectweb.asm.ByteVector::putInt (74 bytes)
113 196 3 jdk.internal.org.objectweb.asm.ByteVector::enlarge (51 bytes)
113 197 3 java.lang.invoke.MemberName::getReferenceKind (12 bytes)
113 198 1 java.lang.invoke.MethodTypeForm::basicType (5 bytes)
113 199 3 java.lang.ClassLoader::checkName (43 bytes)
114 200 3 sun.misc.VM::allowArraySyntax (4 bytes)
115 201 n 0 java.lang.Class::getComponentType (native)
115 202 n 0 java.lang.invoke.MethodHandle::linkToSpecial(LL)V (native) (static)
115 203 3 sun.reflect.misc.ReflectUtil::isVMAnonymousClass (19 bytes)
115 204 3 java.util.concurrent.ConcurrentHashMap::addCount (292 bytes)
115 205 n 0 java.lang.invoke.MethodHandle::linkToInterface(LLL)I (native) (static)
116 207 3 java.util.concurrent.ConcurrentHashMap::casTabAt (20 bytes)
116 206 3 sun.invoke.util.Wrapper::forBasicType (16 bytes)
116 209 3 sun.invoke.util.BytecodeDescriptor::unparseSig (75 bytes)
117 210 3 jdk.internal.org.objectweb.asm.ClassWriter::newClass (9 bytes)
117 208 3 jdk.internal.org.objectweb.asm.ClassWriter::put122 (15 bytes)
118 211 3 java.util.ArrayList::ensureCapacityInternal (23 bytes)
118 212 3 java.util.ArrayList::ensureExplicitCapacity (26 bytes)
118 213 3 java.util.ArrayList::add (29 bytes)
118 214 3 sun.nio.cs.UTF_8$Decoder::decode (779 bytes)
119 216 n 0 java.lang.Thread::currentThread (native) (static)
Stream : 57870863
答案 0 :(得分：1)
尽管有用，但整个“流式”内容会增加抽象性。这很少是免费的。
在某种程度上，你总是讨价还价“代码质量方面”的表现。大多数时候，性能影响可以忽略不计;或者就像你的情况一样：即使有了抽象，你也可以做得更好，因为非常抽象可以让你轻松地从“单线程”切换到“多线程”。
答案 1 :(得分：0)
如评论中所述，您的基准测试容易出现来自各种来源的错误，并且该链接显示JMH是基准测试的一个很好的工具。但是，为了暂时减轻学习难度，我修改了您的代码以引入迭代，这些迭代显示了JVM工作方式的有趣方面。
public class Main {
private static final String USER_FOLDER = System.getProperty("user.home");
private static final String FOLDER = Paths.get(USER_FOLDER, "Documents").toString();
private static final int ITERATIONS = 10000;
private static List<String> getListOfFiles(boolean shouldPrint) throws Exception {
long startTime = System.nanoTime();
List<String> xmlFileList = new ArrayList<String>();
File[] workspaceFiles = new File(USER_FOLDER).listFiles();
try {
for (File file : workspaceFiles) {
if (!file.toString().contains(FOLDER)) {
xmlFileList.add(file.getAbsolutePath());
}
}
} catch (Exception e) {
e.printStackTrace();
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
if (shouldPrint)
System.out.println("Regular For Loop : " + duration / 1000);
return xmlFileList;
}
private static List<String> getListOfFilesStream(boolean shouldPrint) throws IOException {
long startTime = System.nanoTime();
List<String> listOfFiles;
try (Stream<Path> stream = Files.list(Paths.get(USER_FOLDER))) {
listOfFiles = stream.filter(file -> !file.getFileName().toString().contains(FOLDER))
.map(Path::toString)
.collect(Collectors.toList());
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
if (shouldPrint)
System.out.println("Stream : " + duration / 1000);
return listOfFiles;
}
private static List<String> getListOfFilesParallel(boolean shouldPrint) throws IOException {
long startTime = System.nanoTime();
List<String> listOfFiles;
try (Stream<Path> stream = Files.list(Paths.get(USER_FOLDER))) {
listOfFiles = stream.parallel()
.filter(file -> !file.getFileName().toString().contains(FOLDER))
.map(Path::toString)
.collect(Collectors.toList());
}
long endTime = System.nanoTime();
long duration = (endTime - startTime);
if (shouldPrint)
System.out.println("Parallel Stream : " + duration / 1000);
return listOfFiles;
}
public static void main(String[] args) throws Exception {
for (int i = 1; i <= ITERATIONS; i++)
getListOfFiles(i <= 3 || i > ITERATIONS - 3);
for (int i = 1; i <= ITERATIONS; i++)
getListOfFilesParallel(i <= 3 || i > ITERATIONS - 3);
for (int i = 1; i <= ITERATIONS; i++)
getListOfFilesStream(i <= 3 || i > ITERATIONS - 3);
}
}
我更改了方法，仅打印前3次和后3次迭代的时间。结果如下：
Regular For Loop : 508
Regular For Loop : 526
Regular For Loop : 351
Regular For Loop : 180
Regular For Loop : 245
Regular For Loop : 201
Parallel Stream : 6190
Parallel Stream : 854
Parallel Stream : 533
Parallel Stream : 132
Parallel Stream : 255
Parallel Stream : 193
Stream : 1270
Stream : 287
Stream : 267
Stream : 130
Stream : 178
Stream : 168
这表明，一旦对流代码进行JIT编译，至少在我的特定机器上，它平均比
要使JVM编译方法，您需要运行10,000次左右。这取决于JVM版本。您可以在设置上尝试一下，看看会发生什么。