?面試官瘋了：While(true)和For(;;)哪個性能好？
作者：Hollis
有人愿意用While(true)因為他更清晰的看出來這里是個無限循環(huán)。有人愿意用For(;;)，因為有些IDE對于While(true)會給出警告。至于你，愛用啥用啥！
while(true)和for(;;)都是做無限循環(huán)的代碼，他倆有啥區(qū)別呢？
我承認這個問題有點無聊，并且工作中也不會有人刻意的去考慮他們之間的性能差異，也不太會有人在做這個選擇之間糾結。
但是，最近竟然有很多面試官開始問這個問題，所以，那就索性理性分析一波。
準備2段代碼：
public class HollisTest {
public static void main(String[] args) {
for(;;){
System.out.println("this is hollis testing....");
}
}
}public class HollisTest {
public static void main(String[] args) {
while (true){
System.out.println("this is hollis testing....");
}
}
}關于這個問題，網(wǎng)上有很多討論，說那么多沒用，直接反編譯，看看字節(jié)碼有啥區(qū)別就行了。
分別將他們編譯成class文件：
javac HollisTest.java然后再通過javap對class文件進行反編譯，然后我們就會發(fā)現(xiàn)，兩個文件內(nèi)容，一模一樣！??！
Classfile /Users/hollis/workspace/chaojue/HLab/src/main/java/HollisTest.class
Last modified 2023-6-18; size 463 bytes
MD5 checksum 38eddb7d25748625d7c9aa377b6f66d3
Compiled from "HollisTest.java"
public class HollisTest
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #6.#16 // java/lang/Object."<init>":()V
#2 = Fieldref #17.#18 // java/lang/System.out:Ljava/io/PrintStream;
#3 = String #19 // this is hollis testing....
#4 = Methodref #20.#21 // java/io/PrintStream.println:(Ljava/lang/String;)V
#5 = Class #22 // HollisTest
#6 = Class #23 // java/lang/Object
#7 = Utf8 <init>
#8 = Utf8 ()V
#9 = Utf8 Code
#10 = Utf8 LineNumberTable
#11 = Utf8 main
#12 = Utf8 ([Ljava/lang/String;)V
#13 = Utf8 StackMapTable
#14 = Utf8 SourceFile
#15 = Utf8 HollisTest.java
#16 = NameAndType #7:#8 // "<init>":()V
#17 = Class #24 // java/lang/System
#18 = NameAndType #25:#26 // out:Ljava/io/PrintStream;
#19 = Utf8 this is hollis testing....
#20 = Class #27 // java/io/PrintStream
#21 = NameAndType #28:#29 // println:(Ljava/lang/String;)V
#22 = Utf8 HollisTest
#23 = Utf8 java/lang/Object
#24 = Utf8 java/lang/System
#25 = Utf8 out
#26 = Utf8 Ljava/io/PrintStream;
#27 = Utf8 java/io/PrintStream
#28 = Utf8 println
#29 = Utf8 (Ljava/lang/String;)V
{
public HollisTest();
descriptor: ()V
flags: ACC_PUBLIC
Code:
stack=1, locals=1, args_size=1
0: aload_0
1: invokespecial #1 // Method java/lang/Object."<init>":()V
4: return
LineNumberTable:
line 1: 0
public static void main(java.lang.String[]);
descriptor: ([Ljava/lang/String;)V
flags: ACC_PUBLIC, ACC_STATIC
Code:
stack=2, locals=1, args_size=1
0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;
3: ldc #3 // String this is hollis testing....
5: invokevirtual #4 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
8: goto 0
LineNumberTable:
line 5: 0
StackMapTable: number_of_entries = 1
frame_type = 0 /* same */
}
SourceFile: "HollisTest.java"可以看到，兩個用法，其實都是通過goto來干的，所以，這兩者其實是沒啥區(qū)別的。用哪個都行
有人愿意用while(true)因為他更清晰的看出來這里是個無限循環(huán)。有人愿意用for(;;)，因為有些IDE對于while(true)會給出警告。至于你，愛用啥用啥！
責任編輯：姜華
來源：
Hollis
