Enum 분석

1.       Enum 이란 

 

 

 

 

2.       Enum 코드

public enum Operation {


    PLUS("+") {
        @Override
        double apply(double x, double y) {
            return x-y;
        }

    }, MINUS("-") {
        @Override
        double apply(double x, double y) {
            return x-y;
        }

    }, TIMES("*") {
        @Override
        double apply(double x, double y) {
            return x*y;
        }

    }, DIVIDE("/") {
        @Override
        double apply(double x, double y) {
            return x/y;
        }

    };

    private final String symbol;

    Operation(String symbol) {
        this.symbol = symbol;
    }

    abstract double apply(double x, double y);

}

 

3.       Enum 바이트 코드 분석

 

 

Enum 클래스를 생성하게 되면 bytecode 시점에서는

enum 추상 클래스로 생성되면서 Enum 클래스의 상속을 받는다.

Enum 자료형은 모두 public static final enum Enum자료명으로 된다.

Static enum 형태로 내부 클래스로 선언된 되는데 밑에 보면 PlUS , MINUS, TIMES, DIVICE 라고 선언한

// class version 52.0 (52)

// access flags 0x4421

// signature Ljava/lang/Enum<Lcom/study/enum01/Operation;>;

// declaration: com/study/enum01/Operation extends java.lang.Enum<com.study.enum01.Operation>

public abstract enum com/study/enum01/Operation extends java/lang/Enum  { 



// compiled from: Operation.java

// access flags 0x4008

static enum INNERCLASS com/study/enum01/Operation$4 null null

// access flags 0x4008

static enum INNERCLASS com/study/enum01/Operation$3 null null

// access flags 0x4008

static enum INNERCLASS com/study/enum01/Operation$2 null null

// access flags 0x4008

static enum INNERCLASS com/study/enum01/Operation$1 null null



// access flags 0x4019

public final static enum Lcom/study/enum01/Operation; PLUS



// access flags 0x4019

public final static enum Lcom/study/enum01/Operation; MINUS



// access flags 0x4019

public final static enum Lcom/study/enum01/Operation; TIMES



// access flags 0x4019

public final static enum Lcom/study/enum01/Operation; DIVIDE



// access flags 0x12

private final Ljava/lang/String; symbol



// access flags 0x101A

private final static synthetic [Lcom/study/enum01/Operation; $VALUES



// access flags 0x9

public static values()[Lcom/study/enum01/Operation;

        L0

        LINENUMBER 6 L0

        GETSTATIC com/study/enum01/Operation.$VALUES : [Lcom/study/enum01/Operation;

        INVOKEVIRTUAL [Lcom/study/enum01/Operation;.clone ()Ljava/lang/Object;

        CHECKCAST [Lcom/study/enum01/Operation;

        ARETURN

        MAXSTACK = 1

        MAXLOCALS = 0



// access flags 0x9

public static valueOf(Ljava/lang/String;)Lcom/study/enum01/Operation;

        L0

        LINENUMBER 6 L0

        LDC Lcom/study/enum01/Operation;.class

ALOAD 0

        INVOKESTATIC java/lang/Enum.valueOf (Ljava/lang/Class;Ljava/lang/String;)Ljava/lang/Enum;

        CHECKCAST com/study/enum01/Operation

        ARETURN

        L1

        LOCALVARIABLE name Ljava/lang/String; L0 L1 0

        MAXSTACK = 2

        MAXLOCALS = 1



// access flags 0x2

// signature (Ljava/lang/String;)V

// declaration: void <init>(java.lang.String)

private <init>(Ljava/lang/String;ILjava/lang/String;)V

        L0

        LINENUMBER 37 L0

        ALOAD 0

        ALOAD 1

        ILOAD 2

        INVOKESPECIAL java/lang/Enum.<init> (Ljava/lang/String;I)V

        L1

        LINENUMBER 38 L1

        ALOAD 0

        ALOAD 3

        PUTFIELD com/study/enum01/Operation.symbol : Ljava/lang/String;

        L2

        LINENUMBER 39 L2

        RETURN

        L3

        LOCALVARIABLE this Lcom/study/enum01/Operation; L0 L3 0

        LOCALVARIABLE symbol Ljava/lang/String; L0 L3 3

        MAXSTACK = 3

        MAXLOCALS = 4



// access flags 0x400

abstract apply(DD)D



        // access flags 0x1000

        synthetic <init>(Ljava/lang/String;ILjava/lang/String;Lcom/study/enum01/Operation$1;)V

        L0

        LINENUMBER 6 L0

        ALOAD 0

        ALOAD 1

        ILOAD 2

        ALOAD 3

        INVOKESPECIAL com/study/enum01/Operation.<init> (Ljava/lang/String;ILjava/lang/String;)V

        RETURN

        L1

        LOCALVARIABLE this Lcom/study/enum01/Operation; L0 L1 0

        LOCALVARIABLE x0 Ljava/lang/String; L0 L1 1

        LOCALVARIABLE x1 I L0 L1 2

        LOCALVARIABLE x2 Ljava/lang/String; L0 L1 3

        LOCALVARIABLE x3 Lcom/study/enum01/Operation$1; L0 L1 4

        MAXSTACK = 4

        MAXLOCALS = 5



// access flags 0x8

static <clinit>()V

        L0

        LINENUMBER 9 L0

        NEW com/study/enum01/Operation$1

        DUP

        LDC "PLUS"

        ICONST_0

        LDC "+"

        INVOKESPECIAL com/study/enum01/Operation$1.<init> (Ljava/lang/String;ILjava/lang/String;)V

        PUTSTATIC com/study/enum01/Operation.PLUS : Lcom/study/enum01/Operation;

        L1

        LINENUMBER 15 L1

        NEW com/study/enum01/Operation$2

        DUP

        LDC "MINUS"

        ICONST_1

        LDC "-"

        INVOKESPECIAL com/study/enum01/Operation$2.<init> (Ljava/lang/String;ILjava/lang/String;)V

        PUTSTATIC com/study/enum01/Operation.MINUS : Lcom/study/enum01/Operation;

        L2

        LINENUMBER 21 L2

        NEW com/study/enum01/Operation$3

        DUP

        LDC "TIMES"

        ICONST_2

        LDC "*"

        INVOKESPECIAL com/study/enum01/Operation$3.<init> (Ljava/lang/String;ILjava/lang/String;)V

        PUTSTATIC com/study/enum01/Operation.TIMES : Lcom/study/enum01/Operation;

        L3

        LINENUMBER 27 L3

        NEW com/study/enum01/Operation$4

        DUP

        LDC "DIVIDE"

        ICONST_3

        LDC "/"

        INVOKESPECIAL com/study/enum01/Operation$4.<init> (Ljava/lang/String;ILjava/lang/String;)V

        PUTSTATIC com/study/enum01/Operation.DIVIDE : Lcom/study/enum01/Operation;

        L4

        LINENUMBER 6 L4

        ICONST_4

        ANEWARRAY com/study/enum01/Operation

        DUP

        ICONST_0

        GETSTATIC com/study/enum01/Operation.PLUS : Lcom/study/enum01/Operation;

        AASTORE

        DUP

        ICONST_1

        GETSTATIC com/study/enum01/Operation.MINUS : Lcom/study/enum01/Operation;

        AASTORE

        DUP

        ICONST_2

        GETSTATIC com/study/enum01/Operation.TIMES : Lcom/study/enum01/Operation;

        AASTORE

        DUP

        ICONST_3

        GETSTATIC com/study/enum01/Operation.DIVIDE : Lcom/study/enum01/Operation;

        AASTORE

        PUTSTATIC com/study/enum01/Operation.$VALUES : [Lcom/study/enum01/Operation;

        RETURN

        MAXSTACK = 5

        MAXLOCALS = 0

        }