Java Enum

基礎篇，參考這篇文章： Java Enum學習

再給一個例子：

package org.apache.catalina;

/**
 * The list of valid states for components that implement {@link Lifecycle}.
 * See {@link Lifecycle} for the state transition diagram.
 */
public enum LifecycleState {
    NEW(false, null),
    INITIALIZING(false, Lifecycle.BEFORE_INIT_EVENT),
    INITIALIZED(false, Lifecycle.AFTER_INIT_EVENT),
    STARTING_PREP(false, Lifecycle.BEFORE_START_EVENT),
    STARTING(true, Lifecycle.START_EVENT),
    STARTED(true, Lifecycle.AFTER_START_EVENT),
    STOPPING_PREP(true, Lifecycle.BEFORE_STOP_EVENT),
    STOPPING(false, Lifecycle.STOP_EVENT),
    STOPPED(false, Lifecycle.AFTER_STOP_EVENT),
    DESTROYING(false, Lifecycle.BEFORE_DESTROY_EVENT),
    DESTROYED(false, Lifecycle.AFTER_DESTROY_EVENT),
    FAILED(false, null),
    MUST_STOP(true, null),
    MUST_DESTROY(false, null);
    
    private final boolean available;
    private final String lifecycleEvent;
    
    private LifecycleState(boolean available, String lifecycleEvent) {
        this.available = available;
        this.lifecycleEvent = lifecycleEvent;
    }
    
    /**
     * May the public methods other than property getters/setters and lifecycle
     * methods be called for a component in this state? It returns
     * <code>true</code> for any component in any of the following states:
     * <ul>
     * <li>{@link #STARTING}</li>
     * <li>{@link #STARTED}</li>
     * <li>{@link #STOPPING_PREP}</li>
     * <li>{@link #MUST_STOP}</li>
     * </ul>
     */
    public boolean isAvailable() {
        return available;
    }
    
    /**
     * 
     */
    public String getLifecycleEvent() {
        return lifecycleEvent;
    }
}