Enum Class
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枚举是个好东西
一、简单的枚举使用
每一个enum都会继承Enum类
原始的Enum只具有两个属性ordinal、name
每一个枚举数据都是枚举对象
枚举可以方便的使用在switch中
public enum Light { RED , GREEN , YELLOW ;}public class App { public static void main(String[] args) { System.out.println(Light.GREEN); System.out.println(Light.GREEN.ordinal()); System.out.println(Light.GREEN.name()); }}输出------GREEN1GREEN二、枚举基本使用
每一个枚举类都可以新加一些属性，然后通过override toString的方法来实现name的映射
public enum Light2 { // 利用构造函数传参 RED ("red"), GREEN ("green"), YELLOW ("yellow"); // 定义私有变量 private String nCode // 构造函数，枚举类型只能为私有 private Light2(String _nCode) { this.nCode1 = _nCode; } @Override public String toString() { return String.valueOf(this.nCode1); }}public class App { public static void main(String[] args) { System.out.println(Light2.GREEN); System.out.println(Light2.GREEN.ordinal()); System.out.println(Light2.GREEN.name()); }}输出---green1GREEN三、枚举映射
将映射关系存入map中
import java.util.HashMap;import java.util.Map;public class Network { public static class NetworkValue { public static final NetworkValue UNKNOWN = new NetworkValue(-1); public static final NetworkValue WIFI = new NetworkValue(1); public static final NetworkValue NETWORK_2G = new NetworkValue(2); public static final NetworkValue NETWORK_3G = new NetworkValue(3); public static final NetworkValue NETWORK_4G = new NetworkValue(4); public static final NetworkValue NETWORK_5G = new NetworkValue(5); public static final NetworkValue OTHER_MOBILE_NETWORK = new NetworkValue(6); private int value = -1; private NetworkValue(int value) { this.value = value; } public int getValue() { return value; } @Override public String toString() { return String.valueOf(value); } @Override public boolean equals(Object obj) { boolean ret = false; if (obj instanceof NetworkValue) { ret = (value == ((NetworkValue)obj).value); } else if (obj instanceof Integer) { ret = (value == (Integer)obj); } return ret; } } public static class NetworkValueDesc { public static final NetworkValueDesc UNKNOWN = new NetworkValueDesc("unknown"); public static final NetworkValueDesc WIFI = new NetworkValueDesc("wifi"); public static final NetworkValueDesc NETWORK_2G = new NetworkValueDesc("2g"); public static final NetworkValueDesc NETWORK_3G = new NetworkValueDesc("3g"); public static final NetworkValueDesc NETWORK_4G = new NetworkValueDesc("4g"); public static final NetworkValueDesc NETWORK_5G = new NetworkValueDesc("5g"); public static final NetworkValueDesc OTHER_MOBILE_NETWORK = new NetworkValueDesc("other"); private String value = null; private NetworkValueDesc(String value) { this.value = value; } @Override public String toString() { return value; } } public static Map<Integer, String> network_value_desc = new HashMap<Integer, String>(); static { network_value_desc.put(NetworkValue.UNKNOWN.getValue(), NetworkValueDesc.UNKNOWN.toString()); network_value_desc.put(NetworkValue.WIFI.getValue(), NetworkValueDesc.WIFI.toString()); network_value_desc.put(NetworkValue.NETWORK_2G.getValue(), NetworkValueDesc.NETWORK_2G.toString()); network_value_desc.put(NetworkValue.NETWORK_3G.getValue(), NetworkValueDesc.NETWORK_3G.toString()); network_value_desc.put(NetworkValue.NETWORK_4G.getValue(), NetworkValueDesc.NETWORK_4G.toString()); network_value_desc.put(NetworkValue.NETWORK_5G.getValue(), NetworkValueDesc.NETWORK_5G.toString()); network_value_desc.put(NetworkValue.OTHER_MOBILE_NETWORK.getValue(), NetworkValueDesc.OTHER_MOBILE_NETWORK.toString()); } public static String getNetwork(String network_str) { int network = NetworkValue.UNKNOWN.getValue(); try { network = Integer.valueOf(network_str); } catch (Exception e){ } return getNetwork(network); } public static String getNetwork(int network) { String ret = network_value_desc.get(network); if (ret == null) { ret = NetworkValueDesc.UNKNOWN.toString(); } return ret; }}abstract class Enum
package java.lang;import java.io.Serializable;import java.io.IOException;import java.io.InvalidObjectException;import java.io.ObjectInputStream;import java.io.ObjectStreamException;/** * This is the common base class of all Java language enumeration types. * * More information about enums, including descriptions of the * implicitly declared methods synthesized by the compiler, can be * found in section 8.9 of * <cite>The Java™ Language Specification</cite>. * * <p> Note that when using an enumeration type as the type of a set * or as the type of the keys in a map, specialized and efficient * {@linkplain java.util.EnumSet set} and {@linkplain * java.util.EnumMap map} implementations are available. * * @param <E> The enum type subclass * @author Josh Bloch * @author Neal Gafter * @see Class#getEnumConstants() * @see java.util.EnumSet * @see java.util.EnumMap * @since 1.5 */public abstract class Enum<E extends Enum<E>> implements Comparable<E>, 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. * * <b>Most programmers should use the {@link #toString} method in * preference to this one, as the toString method may return * a more user-friendly name.</b> 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 * is not 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<E> 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 */ @SuppressWarnings("unchecked") public final Class<E> getDeclaringClass() { Class<?> clazz = getClass(); Class<?> zuper = clazz.getSuperclass(); return (zuper == Enum.class) ? (Class<E>)clazz : (Class<E>)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.) * * <p>Note that for a particular enum type {@code T}, the * implicitly declared {@code public static T valueOf(String)} * method on that enum may be used instead of this method to map * from a name to the corresponding enum constant. All the * constants of an enum type can be obtained by calling the * implicit {@code public static T[] values()} method of that * type. * * @param <T> The enum type whose constant is to be returned * @param enumType the {@code 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 {@code enumType} or {@code name} * is null * @since 1.5 */ public static <T extends Enum<T>> T valueOf(Class<T> 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 constant " + enumType.getCanonicalName() + "." + name); } /** * enum classes cannot have finalize methods. */ protected final void finalize() { } /** * prevent default deserialization */ private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException { throw new InvalidObjectException("can't deserialize enum"); } private void readObjectNoData() throws ObjectStreamException { throw new InvalidObjectException("can't deserialize enum"); }} 0 0
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