取得和配置字段值

当给了一个类的实例时，它可以去使用映射去配置这个类字段的值．如果在正常的情况下不可用时，这将会为我们完成工作．如下：

import java.lang.reflect.Field;
import java.util.Arrays;
import static java.lang.System.out;

enum Tweedle {DEE,DUM}

public class Book {
		public long chapters = 0;
		public String[] characters = {"Alice", "White Rabbit"};
		public Tweedle twin = Tweedle.DEE;
		
		public static void main(String... args) {
				Book book = new Book();
				String fmt =  "%6s: %-12s = %s%n";
				
				try {
						Class<?> c = book.getClass();
						Field chap = c.getDeclaredField("chapters");
						out.format(fmt, "before", "chapters",book.chapters);
						chap.setLong(book,12);
						out.format(fmt,"after","chapters",chap.getLong(book));
						
						Field chars = c.getDeclaredField("characters");
						out.format(fmt,"before","characters",Arrays.asList(book.characters));
						String[] newChars = {"Queen","King"};
						chars.set(book,newChars);
						out.format(fmt,"after","characters",Arrays.asList(book.characters));
						Field t = c.getDeclaredField("twin");
						out.format(fmt,"before","twin",book.twin);
						t.set(book,Tweedle.DUM);
						out.format(fmt,"after","twin",t.get(book));
				} catch(NoSuchFieldException x) {
						x.printStackTrace();	
				} catch(IllegalAccessException x) {
						x.printStackTrace();	
				}
		}	
}