我一直试图找出一种方法来从我的基类中标记几个方法，以便客户端类可以通过标记来调用它们。示例代码是：
public class Base {
public void method1(){
..change state of base class
}
public void method2(){
..change state of base class
}
public void method3(){
..change state of base class
}
}
main（）方法的客户端类将通过随机指令序列调用Base的每个方法：
public static void main(String[] args) {
String sequence = "ABCAABBBABACCACC"
Base aBase = new Base();
for (int i = 0; i < sequence.length(); i++){
char temp = sequence.charAt(i);
switch(temp){
case 'A':{aBase.method1(); break;}
case 'B':{aBase.method2(); break;}
case 'C':{aBase.method3(); break;} }
}
System.out.println(aBase.getState());
}
现在我希望从Client对象中完全删除switch语句。我知道通过多态替换switch的技术，但是希望避免创建一组新类。我希望简单地将这些方法存储在适当的数据结构中，并以某种方式用序列中的匹配字符标记它们。
地图可以轻松地存储具有值/键对的对象，这些对象可以完成工作（如我所做的here）或命令模式，但由于我不想用对象替换这些方法，是否存在一种不同的方式来存储方法并让客户有选择地调用它们？
感谢任何建议
答案 0 :(得分：6)
这样的东西？
public class Base {
private final Map<Character, Method> methods = new HashMap<Character, Method>();
public Base() throws SecurityException, NoSuchMethodException {
methods.put('A', getClass().getMethod("method1"));
methods.put('B', getClass().getMethod("method2"));
methods.put('C', getClass().getMethod("method3"));
}
public Method getMethod(char c) {
return methods.get(c);
}
public void method1() {}
public void method2() {}
public void method3() {}
}
然后
public static void main(String[] args) throws Exception {
String sequence = "ABCAABBBABACCACC";
Base aBase = new Base();
for (int i = 0; i < sequence.length(); i++) {
char temp = sequence.charAt(i);
aBase.getMethod(temp).invoke(aBase);
}
}
答案 1 :(得分：5)
我会对有问题的方法使用annotations，允许将其标记为“标记方法”，并提供用于该方法的标记字符串。
从那时起，实施变得更加简单;你可以使用反射来迭代类的方法并检查它们的注释;也许在启动时静态地执行此操作并填充从标记字符串到java.lang.reflect.Method的映射。
然后在处理命令字符串时，调用与每个标记对应的方法。
编辑：一些示例代码：
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
@interface TaggedMethod {
String tag();
}
然后在基类中：
public class Base {
@TaggedMethod(tag = "A")
public void method1(){
..change state of base class
}
@TaggedMethod(tag = "B")
public void method2(){
..change state of base class
}
@TaggedMethod(tag = "C")
public void method3(){
..change state of base class
}
}
......并且在客户端：
private static final Map<String, Method> taggedMethods = new HashMap<String, Method>();
// Set up the tag mapping
static
{
for (Method m : Base.class.getDeclaredMethods())
{
TaggedMethod annotation = m.getAnnotation(TaggedMethod.class)
if (annotation != null)
{
taggedMethods.put(annotation.tag(), m);
}
}
}
以便您可以访问：
public static void main(String[] args) throws Exception
{
String sequence = "ABCAABBBABACCACC"
Base aBase = new Base();
for (int i = 0; i < sequence.length(); i++)
{
String temp = sequence.substring(i,1);
Method method = taggedMethods.get(temp);
if (method != null)
{
// Error handling of invocation exceptions not included
method.invoke(aBase);
}
else
{
// Unrecognised tag - handle however
}
}
System.out.println(aBase.getState());
}
此代码尚未编译或测试，顺便说一下......： - ）
答案 2 :(得分：1)
您可以在C＃中使用属性。对于Java，请使用注释。从Attribute类派生一个类，比如TagAttribute，并将该属性应用于方法。
[global::System.AttributeUsage(AttributeTargets.Method, Inherited = true, AllowMultiple = false)]
public sealed class TagAttribute : Attribute
{
public TagAttribute(char value)
{
this.value = value;
}
private char value;
public char Value
{
get { return value; }
}
}
将属性应用于方法：
public class MyClass
{
[Tag('A')]
public void Method1()
{ Console.Write("a"); }
[Tag('B')]
public void Method2()
{ Console.Write("b"); }
[Tag('C')]
public void Method3()
{ Console.Write("c"); }
}
使用反射调用方法：
private static void CallTaggedMethod(MyClass instance, char value)
{
MethodInfo methodToCall = null;
// From the MyClass type...
Type t = typeof(MyClass);
// ...get all methods.
MethodInfo[] methods = t.GetMethods();
// For each method...
foreach (MethodInfo mi in methods)
{
// ...find all TagAttributes applied to it.
TagAttribute[] attributes = (TagAttribute[])mi.GetCustomAttributes(typeof(TagAttribute), true);
if (attributes.Length == 0)
// No attributes, continue.
continue;
// We assume that at most one attribute is applied to each method.
TagAttribute attr = attributes[0];
if (attr.Value == value)
{
// The values match, so we call this method.
methodToCall = mi;
break;
}
}
if (methodToCall == null)
throw new InvalidOperationException("No method to call.");
object result = methodToCall.Invoke(
// Instance object
instance,
// Arguments
new object[0]);
// 'result' now contains the return value.
// It is ignored here.
}
从Main方法调用CallTaggedMethod：
static void Main(string[] args)
{
String sequence = "ABCAABBBABACCACC";
MyClass inst = new MyClass();
foreach(char c in sequence)
CallTaggedMethod(inst, c);
// The rest.
Console.ReadLine();
}
答案 3 :(得分：0)
这是我的注释方法。如果使用注释，甚至不需要方法的Map贴图，只需迭代序列并使用反射查找该标记的方法。
import java.lang.annotation.*;
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
public @interface Tag {
char value();
}
然后：
public class Base {
StringBuilder state = new StringBuilder();
@Tag('A')
public void method1(){
state.append("1");
}
@Tag('B')
public void method2(){
state.append("2");
}
@Tag('C')
public void method3(){
state.append("3");
}
public String getState() {
return state.toString();
}
}
然后
public final class TagRunner {
private TagRunner() {
super();
}
public static void main(String[] args) throws IllegalArgumentException,
IllegalAccessException, InvocationTargetException {
Base b = new Base();
run(b, "ABCAABBBABACCACC");
System.out.println(b.getState());
}
private static <T> void run(T type, String sequence) throws
IllegalArgumentException, IllegalAccessException, InvocationTargetException {
CharacterIterator it = new StringCharacterIterator(sequence);
Class<?> taggedClass = type.getClass();
for (char c = it.first(); c != CharacterIterator.DONE; c = it.next()) {
getMethodForCharacter(taggedClass, c).invoke(type);
}
}
private static Method getMethodForCharacter(Class<?> taggedClass, char c) {
for (Method m : taggedClass.getDeclaredMethods()) {
if (m.isAnnotationPresent(Tag.class)){
char value = m.getAnnotation(Tag.class).value();
if (c == value) {
return m;
}
}
}
//If we get here, there are no methods tagged with this character
return null;
}
}