JAva多態の学習,overloadとoverrideの理解[英語]
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とても良い学习の多态のウェブサイト(英语の)を探し当てて、今贴って、いくつか启発の意义があるかもしれなくて、みんなは兴味があって直接ウェブサイトに入って见て、问题があって评论を歓迎します.https://programmingmitra.blogspot.com/2017/05/how-does-jvm-handle-method-overriding-internally.html学習コース: Everything About ClassNotFoundException Vs NoClassDefFoundError Everything About Method Overloading Vs Method Overriding How Does JVM Handle Method Overloading and Overriding Internally
以下に、チュートリアルに従って実行した結果を一部貼ります.
英語を見たくないなら、下のコードを直接走ってもいいです.注釈を書いたら、何か収穫があるでしょう.
以下に、チュートリアルに従って実行した結果を一部貼ります.
> cmd: G:\Program Files\Java\jdk1.8.0_161\bin>javap -"verbose"
> D:\eclipse-workspace\JavaPuzzler\bin\OverridingInternalExample.class
> Classfile
> /D:/eclipse-workspace/JavaPuzzler/bin/OverridingInternalExample.class
> Last modified 2018-8-3; size 961 bytes MD5 checksum
> 16614163b3e084ea8bd3966c598c2694 Compiled from
> "OverridingInternalExample.java" public class
> OverridingInternalExample minor version: 0 major version: 52
> flags: ACC_PUBLIC, ACC_SUPER Constant pool: #1 = Class
> #2 // OverridingInternalExample #2 = Utf8 OverridingInternalExample #3 = Class #4 //
> java/lang/Object #4 = Utf8 java/lang/Object #5 =
> Utf8 #6 = Utf8 ()V #7 = Utf8
> Code #8 = Methodref #3.#9 //
> java/lang/Object."":()V #9 = NameAndType #5:#6
> // "":()V #10 = Utf8 LineNumberTable #11 =
> Utf8 LocalVariableTable #12 = Utf8 this
> #13 = Utf8 LOverridingInternalExample; #14 = Utf8 main #15 = Utf8 ([Ljava/lang/String;)V #16 = Class
> #17 // OverridingInternalExample$Mammal #17 = Utf8 OverridingInternalExample$Mammal #18 = Methodref #16.#19
> //
> OverridingInternalExample$Mammal."":(LOverridingInternalExample$Mammal;LOverridingInternalExample$Mammal;)V
> #19 = NameAndType #5:#20 // "":(LOverridingInternalExample$Mammal;LOverridingInternalExample$Mammal;)V
> #20 = Utf8 (LOverridingInternalExample$Mammal;LOverridingInternalExample$Mammal;)V
> #21 = Methodref #16.#22 // OverridingInternalExample$Mammal.speak:()V #22 = NameAndType
> #23:#6 // speak:()V #23 = Utf8 speak #24 = Class #25 // OverridingInternalExample$Human
> #25 = Utf8 OverridingInternalExample$Human #26 = Methodref #24.#27 //
> OverridingInternalExample$Human."":(LOverridingInternalExample$Human;)V
> #27 = NameAndType #5:#28 // "":(LOverridingInternalExample$Human;)V #28 = Utf8
> (LOverridingInternalExample$Human;)V #29 = Methodref
> #24.#22 // OverridingInternalExample$Human.speak:()V #30 = String #31 // Hindi #31 = Utf8
> Hindi #32 = Methodref #24.#33 //
> OverridingInternalExample$Human.speak:(Ljava/lang/String;)V #33 =
> NameAndType #23:#34 // speak:(Ljava/lang/String;)V #34
> = Utf8 (Ljava/lang/String;)V #35 = Utf8 args #36 = Utf8 [Ljava/lang/String; #37 = Utf8
> anyMammal #38 = Utf8
> LOverridingInternalExample$Mammal; #39 = Utf8
> humanMammal #40 = Utf8 human #41 = Utf8
> LOverridingInternalExample$Human; #42 = Utf8
> SourceFile #43 = Utf8 OverridingInternalExample.java
> #44 = Utf8 InnerClasses #45 = Utf8 Human #46 = Utf8 Mammal { public OverridingInternalExample();
> descriptor: ()V
> flags: ACC_PUBLIC
> Code:
> stack=1, locals=1, args_size=1
> 0: aload_0
> 1: invokespecial #8 // Method java/lang/Object."":()V
> 4: return
> LineNumberTable:
> line 1: 0
> LocalVariableTable:
> Start Length Slot Name Signature
> 0 5 0 this LOverridingInternalExample;
>
> public static void main(java.lang.String[]);
> descriptor: ([Ljava/lang/String;)V
> flags: ACC_PUBLIC, ACC_STATIC
> Code:
> stack=4, locals=4, args_size=1
> 0: new #16 // class OverridingInternalExample$Mammal
> 3: dup
> 4: aconst_null
> 5: aconst_null
> 6: invokespecial #18 // Method OverridingInternalExample$Mammal."":(LOverridingInternalExample$Mammal;LOverridingInternalExample$Mammal;)V
> 9: astore_1
> 10: aload_1
> 11: invokevirtual #21 // Method OverridingInternalExample$Mammal.speak:()V
> 14: new #24 // class OverridingInternalExample$Human
> 17: dup
> 18: aconst_null
> 19: invokespecial #26 // Method OverridingInternalExample$Human."":(LOverridingInternalExample$Human;)V
> 22: astore_2
> 23: aload_2
> 24: invokevirtual #21 // Method OverridingInternalExample$Mammal.speak:()V
> 27: new #24 // class OverridingInternalExample$Human
> 30: dup
> 31: aconst_null
> 32: invokespecial #26 // Method OverridingInternalExample$Human."":(LOverridingInternalExample$Human;)V
> 35: astore_3
> 36: aload_3
> 37: invokevirtual #29 // Method OverridingInternalExample$Human.speak:()V
> 40: aload_3
> 41: ldc #30 // String Hindi
> 43: invokevirtual #32 // Method OverridingInternalExample$Human.speak:(Ljava/lang/String;)V
> 46: return
> LineNumberTable:
> line 25: 0
> line 26: 10
> line 29: 14
> line 30: 23
> line 33: 27
> line 34: 36
> line 37: 40
> line 39: 46
> LocalVariableTable:
> Start Length Slot Name Signature
> 0 47 0 args [Ljava/lang/String;
> 10 37 1 anyMammal LOverridingInternalExample$Mammal;
> 23 24 2 humanMammal LOverridingInternalExample$Mammal;
> 36 11 3 human LOverridingInternalExample$Human; } SourceFile: "OverridingInternalExample.java"
英語を見たくないなら、下のコードを直接走ってもいいです.注釈を書いたら、何か収穫があるでしょう.
public class OverridingInternalExample {
//reference:https://programmingmitra.blogspot.com/2017/05/how-does-jvm-handle-method-overriding-internally.html
private static class Mammal {
public void speak() { System.out.println("ohlllalalalalalaoaoaoa"); }
}
private static class Human extends Mammal {
@Override
public void speak() { System.out.println("Hello"); }
// Valid overload of speak
public void speak(String language) {
if (language.equals("Hindi")) System.out.println("Namaste");
else System.out.println("Hello");
}
@Override
public String toString() { return "Human Class"; }
}
// cmd:
// G:\Program Files\Java\jdk1.8.0_161\bin>javap -"verbose" D:\eclipse-workspace\JavaPuzzler\bin\OverridingInternalExample.class
// Code below contains the output and and bytecode of the method calls
public static void main(String[] args) {
Mammal anyMammal = new Mammal();
anyMammal.speak(); // Output - ohlllalalalalalaoaoaoa
// 10: invokevirtual #4 // Method org/programming/mitra/exercises/OverridingInternalExample$Mammal.speak:()V
Mammal humanMammal = new Human();
humanMammal.speak(); // Output - Hello
// 23: invokevirtual #4 // Method org/programming/mitra/exercises/OverridingInternalExample$Mammal.speak:()V
Human human = new Human();
human.speak(); // Output - Hello
// 36: invokevirtual #7 // Method org/programming/mitra/exercises/OverridingInternalExample$Human.speak:()V
human.speak("Hindi"); // Output - Namaste
// 42: invokevirtual #9 // Method org/programming/mitra/exercises/OverridingInternalExample$Human.speak:(Ljava/lang/String;)V
}
}
// Human.speak() Human.speak:(Ljava/lang/String;) method，overload
// override， ， anyMammal.speak(); invokevirtual #4 class
// method ， invokevirtual
//Operation invokevirtual accepts a pointer to method reference call ( #4 an index into the constant pool)
//And that method reference #4 again refers to a method name and Class reference
// ：
/**
#4 = Methodref #2.#27 // org/programming/mitra/exercises/OverridingInternalExample$Mammal.speak:()V
#2 = Class #25 // org/programming/mitra/exercises/OverridingInternalExample$Mammal
#25 = Utf8 org/programming/mitra/exercises/OverridingInternalExample$Mammal
#27 = NameAndType #35:#17 // speak:()V
#35 = Utf8 speak
#17 = Utf8
()V
*/
// ，invokevirtual #4 ， #2 #27， #2 #27 （get a reference to）method method class。