Java for each實(shí)現(xiàn)機(jī)制代碼原理解析
源測(cè)試代碼如下
public class ForEachTest { public void test4Iterate(Iterable<String> strings) { for (String str : strings) { System.out.println(str); } } public void test4Array(String[] strings) { for (String str : strings) { System.out.println(str); } }}
執(zhí)行編譯命令
javac ForEachTest.java
使用idea查看反編的Java文件
import java.util.Iterator;public class ForEachTest { public ForEachTest() { } public void test4Iterate(Iterable<String> var1) { Iterator var2 = var1.iterator(); while(var2.hasNext()) { String var3 = (String)var2.next(); System.out.println(var3); } } public void test4Array(String[] var1) { String[] var2 = var1; int var3 = var1.length; for(int var4 = 0; var4 < var3; ++var4) { String var5 = var2[var4]; System.out.println(var5); } }}
執(zhí)行指令查看對(duì)應(yīng)的匯編指令
javap -c ForEachTest.class
Compiled from 'ForEachTest.java'public class ForEachTest { public ForEachTest(); Code: 0: aload_0 1: invokespecial #1 // Method java/lang/Object.'<init>':()V 4: return public void test4Iterate(java.lang.Iterable<java.lang.String>); Code: 0: aload_1 1: invokeinterface #2, 1 // InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator; 6: astore_2 7: aload_2 8: invokeinterface #3, 1 // InterfaceMethod java/util/Iterator.hasNext:()Z 13: ifeq 36 16: aload_2 17: invokeinterface #4, 1 // InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; 22: checkcast #5 // class java/lang/String 25: astore_3 26: getstatic #6 // Field java/lang/System.out:Ljava/io/PrintStream; 29: aload_3 30: invokevirtual #7 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 33: goto 7 36: return public void test4Array(java.lang.String[]); Code: 0: aload_1 1: astore_2 2: aload_2 3: arraylength 4: istore_3 5: iconst_0 6: istore 4 8: iload 4 10: iload_3 11: if_icmpge 34 14: aload_2 15: iload 4 17: aaload 18: astore 5 20: getstatic #6 // Field java/lang/System.out:Ljava/io/PrintStream; 23: aload 5 25: invokevirtual #7 // Method java/io/PrintStream.println:(Ljava/lang/String;)V 28: iinc 4, 1 31: goto 8 34: return}
由反編類和匯編指令可以看到對(duì)于Iterable類,是通過其迭代方法執(zhí)行for each,而對(duì)于數(shù)組是通過傳統(tǒng)的for循環(huán)方式執(zhí)行迭代
因?yàn)榧项惖膄or each是基于迭代器循環(huán)的,所以根據(jù)迭代器實(shí)現(xiàn)的不同,for each的性能也會(huì)不同
以上就是本文的全部?jī)?nèi)容,希望對(duì)大家的學(xué)習(xí)有所幫助,也希望大家多多支持好吧啦網(wǎng)。
相關(guān)文章:
1. python爬蟲實(shí)戰(zhàn)之制作屬于自己的一個(gè)IP代理模塊2. Ajax返回值類型與用法實(shí)例分析3. 使用FormData進(jìn)行Ajax請(qǐng)求上傳文件的實(shí)例代碼4. .Net Core和RabbitMQ限制循環(huán)消費(fèi)的方法5. 解決ajax請(qǐng)求后臺(tái),有時(shí)收不到返回值的問題6. Python編寫nmap掃描工具7. 如何在jsp界面中插入圖片8. HTML 絕對(duì)路徑與相對(duì)路徑概念詳細(xì)9. 基于javaweb+jsp實(shí)現(xiàn)企業(yè)財(cái)務(wù)記賬管理系統(tǒng)10. .NET6打包部署到Windows Service的全過程
