Enum列挙の研究
19681 ワード
Enumというキーワードはjavaでよく知られているし、あまり使われていないからです.実はenumの機能は完全に他の方法で実現することができて、しかしその原理に対して
まだよくわかりません.研究を始めます.
簡単な例を書きます.
enumの宣言は宣言オブジェクトにも宣言クラスにも似ているような気がします.
このクラスをコンパイルすると、2つのクラスが増えることに気づきました.
これにより、enumはクラスだと大胆に推測した.逆コンパイル後、ソースコードを確認します.
EnumTest
EnumTest$CellphoneSystem
EnumTest$SEASON
逆コンパイルされたEnumTestでは,2つのenumが確かに2つのクラスを宣言し,static finalタイプであり,いずれもEnumを継承していることが分かった.
中の対応する変数はすべてpublic static finalタイプで、すべて構造関数があって、すべてvalues()があって、valueOf(String s)方法.
values()では、valueOf(String s)メソッドで上記と同様のクラスが使用されます. EnumTest$CellphoneSystem,EnumTest$SEASON
ソースコードから、enumはコンパイル時に対応するenumクラスfinal staticを宣言していることがわかります.各値はpublic static final変数であり、static
ブロックでコンストラクション関数を呼び出します.
public staticのようにクラス名で直接値を取ることができます
次に、上のEnumTest類を変更し、enumの使い方を研究します.
enumクラスが使用されます.
Pelple
Enumの使用は、特殊なstatic finalクラスとして使用することができます.構造関数が必要で、構造関数でオブジェクトを宣言する必要があります.
普通のクラスのように独自の方法を持つこともできます.このようにenumを使うのは簡単で、理解すればプログラム設計がうまくいく.
---------次はEnumクラスのソースコードです.java.lang.*パッケージでは、研究に興味があります------
まだよくわかりません.研究を始めます.
簡単な例を書きます.
package org.test.algo;
import java.util.EnumMap;
import java.util.EnumSet;
import java.util.Enumeration;
public class EnumTest {
enum CellphoneSystem{Android,IOS,WP8,BLACBERRY,Ubuntu}
// enum SEASON{SPRING("googd"),SUMMER("better"),AUTOMN("best"),WINTER("bad")}
/* ， : The constructor EnumTest.SEASON(String) is undefined
。 ， enum ？
*/
enum SEASON{
SPRING("googd"),SUMMER("better"),AUTOMN("best"),WINTER("bad");
String feel="";
SEASON(String myfeel){
this.feel=myfeel;
}
}
public static void main(String[] sdfs){
}
}
enumの宣言は宣言オブジェクトにも宣言クラスにも似ているような気がします.
このクラスをコンパイルすると、2つのクラスが増えることに気づきました.
これにより、enumはクラスだと大胆に推測した.逆コンパイル後、ソースコードを確認します.
EnumTest
// Decompiled Using: FrontEnd Plus v2.03 and the JAD Engine
// Available From: http://www.reflections.ath.cx
// Decompiler options: packimports(3)
// Source File Name: EnumTest.java
package org.test.algo;
public class EnumTest
{
static final class CellphoneSystem extends Enum
{
public static CellphoneSystem[] values()
{
CellphoneSystem acellphonesystem[];
int i;
CellphoneSystem acellphonesystem1[];
System.arraycopy(acellphonesystem = ENUM$VALUES, 0, acellphonesystem1 = new
CellphoneSystem[i = acellphonesystem.length], 0, i);
return acellphonesystem1;
}
public static CellphoneSystem valueOf(String s)
{
return (CellphoneSystem)Enum.valueOf(org/test/algo/EnumTest$CellphoneSystem, s);
}
public static final CellphoneSystem Android;
public static final CellphoneSystem IOS;
public static final CellphoneSystem WP8;
public static final CellphoneSystem BLACBERRY;
public static final CellphoneSystem Ubuntu;
private static final CellphoneSystem ENUM$VALUES[];
static
{
Android = new CellphoneSystem("Android", 0);
IOS = new CellphoneSystem("IOS", 1);
WP8 = new CellphoneSystem("WP8", 2);
BLACBERRY = new CellphoneSystem("BLACBERRY", 3);
Ubuntu = new CellphoneSystem("Ubuntu", 4);
ENUM$VALUES = (new CellphoneSystem[] {
Android, IOS, WP8, BLACBERRY, Ubuntu
});
}
private CellphoneSystem(String s, int i)
{
super(s, i);
}
}
static final class SEASON extends Enum
{
public static SEASON[] values()
{
SEASON aseason[];
int i;
SEASON aseason1[];
System.arraycopy(aseason = ENUM$VALUES, 0, aseason1 = new SEASON[i = aseason.length],
0, i);
return aseason1;
}
public static SEASON valueOf(String s)
{
return (SEASON)Enum.valueOf(org/test/algo/EnumTest$SEASON, s);
}
public static final SEASON SPRING;
public static final SEASON SUMMER;
public static final SEASON AUTOMN;
public static final SEASON WINTER;
String feel;
private static final SEASON ENUM$VALUES[];
static
{
SPRING = new SEASON("SPRING", 0, "googd");
SUMMER = new SEASON("SUMMER", 1, "better");
AUTOMN = new SEASON("AUTOMN", 2, "best");
WINTER = new SEASON("WINTER", 3, "bad");
ENUM$VALUES = (new SEASON[] {
SPRING, SUMMER, AUTOMN, WINTER
});
}
private SEASON(String s, int i, String myfeel)
{
super(s, i);
feel = "";
feel = myfeel;
}
}
public EnumTest()
{
}
public static void main(String args[])
{
}
}EnumTest$CellphoneSystem
// Decompiled Using: FrontEnd Plus v2.03 and the JAD Engine
// Available From: http://www.reflections.ath.cx
// Decompiler options: packimports(3)
// Source File Name: EnumTest.java
package org.test.algo;
// Referenced classes of package org.test.algo:
// EnumTest
static final class EnumTest$CellphoneSystem extends Enum
{
public static EnumTest$CellphoneSystem[] values()
{
EnumTest$CellphoneSystem aenumtest$cellphonesystem[];
int i;
EnumTest$CellphoneSystem aenumtest$cellphonesystem1[];
System.arraycopy(aenumtest$cellphonesystem = ENUM$VALUES, 0, aenumtest$cellphonesystem1 =
new EnumTest$CellphoneSystem[i = aenumtest$cellphonesystem.length], 0, i);
return aenumtest$cellphonesystem1;
}
public static EnumTest$CellphoneSystem valueOf(String s)
{
return (EnumTest$CellphoneSystem)Enum.valueOf(org/test/algo/EnumTest$CellphoneSystem, s);
}
public static final EnumTest$CellphoneSystem Android;
public static final EnumTest$CellphoneSystem IOS;
public static final EnumTest$CellphoneSystem WP8;
public static final EnumTest$CellphoneSystem BLACBERRY;
public static final EnumTest$CellphoneSystem Ubuntu;
private static final EnumTest$CellphoneSystem ENUM$VALUES[];
static
{
Android = new EnumTest$CellphoneSystem("Android", 0);
IOS = new EnumTest$CellphoneSystem("IOS", 1);
WP8 = new EnumTest$CellphoneSystem("WP8", 2);
BLACBERRY = new EnumTest$CellphoneSystem("BLACBERRY", 3);
Ubuntu = new EnumTest$CellphoneSystem("Ubuntu", 4);
ENUM$VALUES = (new EnumTest$CellphoneSystem[] {
Android, IOS, WP8, BLACBERRY, Ubuntu
});
}
private EnumTest$CellphoneSystem(String s, int i)
{
super(s, i);
}
}EnumTest$SEASON
// Decompiled Using: FrontEnd Plus v2.03 and the JAD Engine
// Available From: http://www.reflections.ath.cx
// Decompiler options: packimports(3)
// Source File Name: EnumTest.java
package org.test.algo;
// Referenced classes of package org.test.algo:
// EnumTest
static final class EnumTest$SEASON extends Enum
{
public static EnumTest$SEASON[] values()
{
EnumTest$SEASON aenumtest$season[];
int i;
EnumTest$SEASON aenumtest$season1[];
System.arraycopy(aenumtest$season = ENUM$VALUES, 0, aenumtest$season1 = new
EnumTest$SEASON[i = aenumtest$season.length], 0, i);
return aenumtest$season1;
}
public static EnumTest$SEASON valueOf(String s)
{
return (EnumTest$SEASON)Enum.valueOf(org/test/algo/EnumTest$SEASON, s);
}
public static final EnumTest$SEASON SPRING;
public static final EnumTest$SEASON SUMMER;
public static final EnumTest$SEASON AUTOMN;
public static final EnumTest$SEASON WINTER;
String feel;
private static final EnumTest$SEASON ENUM$VALUES[];
static
{
SPRING = new EnumTest$SEASON("SPRING", 0, "googd");
SUMMER = new EnumTest$SEASON("SUMMER", 1, "better");
AUTOMN = new EnumTest$SEASON("AUTOMN", 2, "best");
WINTER = new EnumTest$SEASON("WINTER", 3, "bad");
ENUM$VALUES = (new EnumTest$SEASON[] {
SPRING, SUMMER, AUTOMN, WINTER
});
}
private EnumTest$SEASON(String s, int i, String myfeel)
{
super(s, i);
feel = "";
feel = myfeel;
}
}逆コンパイルされたEnumTestでは,2つのenumが確かに2つのクラスを宣言し,static finalタイプであり,いずれもEnumを継承していることが分かった.
中の対応する変数はすべてpublic static finalタイプで、すべて構造関数があって、すべてvalues()があって、valueOf(String s)方法.
values()では、valueOf(String s)メソッドで上記と同様のクラスが使用されます. EnumTest$CellphoneSystem,EnumTest$SEASON
ソースコードから、enumはコンパイル時に対応するenumクラスfinal staticを宣言していることがわかります.各値はpublic static final変数であり、static
ブロックでコンストラクション関数を呼び出します.
public staticのようにクラス名で直接値を取ることができます
次に、上のEnumTest類を変更し、enumの使い方を研究します.
package org.test.algo;
import java.util.EnumMap;
import java.util.EnumSet;
import java.util.Enumeration;
import java.util.Iterator;
public class EnumTest {
enum CellphoneSystem{Android,IOS,WP8,BLACBERRY,Ubuntu};
// enum SEASON{SPRING("googd"),SUMMER("better"),AUTOMN("best"),WINTER("bad")}
/* ， : The constructor EnumTest.SEASON(String) is undefined
。 ， enum ？
*/
enum SEASON{
SPRING("googd"),SUMMER("better"),AUTOMN("best"),WINTER("bad");//
String feel="";
//
SEASON(String myfeel){
this.feel=myfeel;
}
// get,set
public String getFeel() {
return feel;
}
public void setFeel(String feel) {
this.feel = feel;
}
// ， 。
public static SEASON whichlevel(String level){
SEASON res=null;
if(level==null){
}else{
if(level.trim().equals("A")){
res=SPRING;
}else if(level.trim().equals("B")){
res=SUMMER;
}else if(level.trim().equals("C")){
res=AUTOMN;
}else if(level.trim().equals("D")){
res=WINTER;
}
}
return res;
}
};
public static void main(String[] sdfs){
//1
// EnumTest.SEASON[] seasons= EnumTest.SEASON.values();//
SEASON[] seasons= SEASON.values();
for(SEASON se:seasons){
System.out.println(se.ordinal()+","+se+","+se.toString()+","+se.getFeel());
}
//2
System.out.println("-----------------------------");
System.out.println(EnumTest.SEASON.SUMMER);//SUMMER
System.out.println(EnumTest.SEASON.AUTOMN.getFeel());//best
EnumTest.SEASON.SUMMER.setFeel("awesome");
System.out.println(EnumTest.SEASON.SUMMER.getFeel());//awesome
System.out.println(EnumTest.SEASON.SUMMER.whichlevel("C"));//AUTOMN
System.out.println(EnumTest.SEASON.valueOf("WINTER"));//WINTER
System.out.println(EnumTest.SEASON.WINTER.getDeclaringClass());//class org.test.algo.EnumTest$SEASON
//3 enum public enum Pelple
System.out.println("-----------------------------");
System.out.println(Pelple.SEX+"--"+Pelple.SEX.getSexValueOfpeople());
Pelple.SEX.setFlag(false);
System.out.println(Pelple.SEX+"--"+Pelple.SEX.getSexValueOfpeople());
//4,EnumMap
System.out.println("-----------------------------");
EnumMap emap=new EnumMap(EnumTest.SEASON.class);
emap.put(EnumTest.SEASON.SPRING, " ");
emap.put(EnumTest.SEASON.SUMMER, " ");
emap.put(EnumTest.SEASON.AUTOMN, " ");
emap.put(EnumTest.SEASON.WINTER, " ");
System.out.println(emap.get(EnumTest.SEASON.SUMMER));
System.out.println("-----");
// map
for(Iterator it=emap.keySet().iterator();it.hasNext();){
Object key=it.next();
Object value=emap.get(key);
System.out.println("key:"+key+",value:"+value);
}
}
}
/*
：
0,SPRING,SPRING,googd
1,SUMMER,SUMMER,better
2,AUTOMN,AUTOMN,best
3,WINTER,WINTER,bad
-----------------------------
SUMMER
best
awesome
AUTOMN
WINTER
class org.test.algo.EnumTest$SEASON
-----------------------------
SEX--
SEX--
-----------------------------
-----
key:SPRING,value:
key:SUMMER,value:
key:AUTOMN,value:
key:WINTER,value:
;
EnumTest.SEASON.WINTER ：class org.test.algo.EnumTest$SEASON
EnumTest
enum ， 。
; ;
enum CellphoneSystem{Android,IOS,WP8,BLACBERRY,Ubuntu}
enum CellphoneSystem{Android,IOS,WP8,BLACBERRY,Ubuntu}; 。
EnumTest enum， 。
enum （ class ）
public enum Pelple.
*/
enumクラスが使用されます.
Pelple
package org.test.algo;
public enum Pelple {
SEX(true);
boolean flag=false;
Pelple(boolean f){
this.flag=f;
}
public String getSexValueOfpeople(){
String res=" ";
if(this.isFlag()){
res=" ";
}else{
res=" ";
}
return res;
}
public boolean isFlag() {
return flag;
}
public void setFlag(boolean flag) {
this.flag = flag;
}
}
Enumの使用は、特殊なstatic finalクラスとして使用することができます.構造関数が必要で、構造関数でオブジェクトを宣言する必要があります.
普通のクラスのように独自の方法を持つこともできます.このようにenumを使うのは簡単で、理解すればプログラム設計がうまくいく.
---------次はEnumクラスのソースコードです.java.lang.*パッケージでは、研究に興味があります------
/*
* @(#)Enum.java 1.15 06/01/27
*
* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
import java.io.Serializable;
/**
* This is the common base class of all Java language enumeration types.
*
* @author Josh Bloch
* @author Neal Gafter
* @version 1.15, 01/27/06
* @since 1.5
*/
public abstract class Enum>
implements Comparable, Serializable {
/**
* The name of this enum constant, as declared in the enum declaration.
* Most programmers should use the {@link #toString} method rather than
* accessing this field.
*/
private final String name;
/**
* Returns the name of this enum constant, exactly as declared in its
* enum declaration.
*
* Most programmers should use the {@link #toString} method in
* preference to this one, as the toString method may return
* a more user-friendly name. This method is designed primarily for
* use in specialized situations where correctness depends on getting the
* exact name, which will not vary from release to release.
*
* @return the name of this enum constant
*/
public final String name() {
return name;
}
/**
* The ordinal of this enumeration constant (its position
* in the enum declaration, where the initial constant is assigned
* an ordinal of zero).
*
* Most programmers will have no use for this field. It is designed
* for use by sophisticated enum-based data structures, such as
* {@link java.util.EnumSet} and {@link java.util.EnumMap}.
*/
private final int ordinal;
/**
* Returns the ordinal of this enumeration constant (its position
* in its enum declaration, where the initial constant is assigned
* an ordinal of zero).
*
* Most programmers will have no use for this method. It is
* designed for use by sophisticated enum-based data structures, such
* as {@link java.util.EnumSet} and {@link java.util.EnumMap}.
*
* @return the ordinal of this enumeration constant
*/
public final int ordinal() {
return ordinal;
}
/**
* Sole constructor. Programmers cannot invoke this constructor.
* It is for use by code emitted by the compiler in response to
* enum type declarations.
*
* @param name - The name of this enum constant, which is the identifier
* used to declare it.
* @param ordinal - The ordinal of this enumeration constant (its position
* in the enum declaration, where the initial constant is assigned
* an ordinal of zero).
*/
protected Enum(String name, int ordinal) {
this.name = name;
this.ordinal = ordinal;
}
/**
* Returns the name of this enum constant, as contained in the
* declaration. This method may be overridden, though it typically
* isn't necessary or desirable. An enum type should override this
* method when a more "programmer-friendly" string form exists.
*
* @return the name of this enum constant
*/
public String toString() {
return name;
}
/**
* Returns true if the specified object is equal to this
* enum constant.
*
* @param other the object to be compared for equality with this object.
* @return true if the specified object is equal to this
* enum constant.
*/
public final boolean equals(Object other) {
return this==other;
}
/**
* Returns a hash code for this enum constant.
*
* @return a hash code for this enum constant.
*/
public final int hashCode() {
return super.hashCode();
}
/**
* Throws CloneNotSupportedException. This guarantees that enums
* are never cloned, which is necessary to preserve their "singleton"
* status.
*
* @return (never returns)
*/
protected final Object clone() throws CloneNotSupportedException {
throw new CloneNotSupportedException();
}
/**
* Compares this enum with the specified object for order. Returns a
* negative integer, zero, or a positive integer as this object is less
* than, equal to, or greater than the specified object.
*
* Enum constants are only comparable to other enum constants of the
* same enum type. The natural order implemented by this
* method is the order in which the constants are declared.
*/
public final int compareTo(E o) {
Enum other = (Enum)o;
Enum self = this;
if (self.getClass() != other.getClass() && // optimization
self.getDeclaringClass() != other.getDeclaringClass())
throw new ClassCastException();
return self.ordinal - other.ordinal;
}
/**
* Returns the Class object corresponding to this enum constant's
* enum type. Two enum constants e1 and e2 are of the
* same enum type if and only if
* e1.getDeclaringClass() == e2.getDeclaringClass().
* (The value returned by this method may differ from the one returned
* by the {@link Object#getClass} method for enum constants with
* constant-specific class bodies.)
*
* @return the Class object corresponding to this enum constant's
* enum type
*/
public final Class getDeclaringClass() {
Class clazz = getClass();
Class zuper = clazz.getSuperclass();
return (zuper == Enum.class) ? clazz : zuper;
}
/**
* Returns the enum constant of the specified enum type with the
* specified name. The name must match exactly an identifier used
* to declare an enum constant in this type. (Extraneous whitespace
* characters are not permitted.)
*
* @param enumType the Class object of the enum type from which
* to return a constant
* @param name the name of the constant to return
* @return the enum constant of the specified enum type with the
* specified name
* @throws IllegalArgumentException if the specified enum type has
* no constant with the specified name, or the specified
* class object does not represent an enum type
* @throws NullPointerException if enumType or name
* is null
* @since 1.5
*/
public static > T valueOf(Class enumType,
String name) {
T result = enumType.enumConstantDirectory().get(name);
if (result != null)
return result;
if (name == null)
throw new NullPointerException("Name is null");
throw new IllegalArgumentException(
"No enum const " + enumType +"." + name);
}
/**
* enum classes cannot have finalize methods.
*/
protected final void finalize() { }
}