利用反射，输出类的所有信息

水深无声 2022-07-17 02:57 112阅读 0赞

下面是我写的一个利用反射来调用类的所有信息的例子。包括再运行这个程序的时候遇到的问题，和请教stack overflow 之后得到的一些回答，希望可以和大家一起分享一下经验。

package reflect;
    
    import java.lang.reflect.Constructor;
    import java.lang.reflect.Field;
    import java.lang.reflect.Method;
    import java.lang.reflect.Modifier;
    
    public class ClassViewer {
        public static void view(String clazName) throws ClassNotFoundException{
            Class clz=Class.forName(clazName);
            Package p=clz.getPackage();
            System.out.printf("package %s;%n", clz.getName());
    
            int modifier=clz.getModifiers();//取得类型的修饰常数
            System.out.printf("%s %s %s {%n", 
                    Modifier.toString(modifier),
                    Modifier.isInterface(modifier) ? "interface" :"class",
                    clz.getName()
                    );
    
            //取得声明的数据成员代表对象
            Field[] fields =clz.getDeclaredFields();
            for(Field field:fields){
                //显示权限修饰
                System.out.printf("\t%s %s %s;%n", 
                        Modifier.toString(field.getModifiers()),
                        field.getType().getName(),
                        field.getName()
                        );
            }
    
            //取得声明的创建方法代表对象
            Constructor[] constructors=clz.getDeclaredConstructors();
            for(Constructor constructor:constructors){
                System.out.printf("\t%s %s();%n", 
                        Modifier.toString(constructor.getModifiers()),
                        constructor.getName()
                        );
            }
    
            //取得声明的方法成员代表对象
            Method[] methods=clz.getDeclaredMethods();
            for(Method method:methods){
                System.out.printf("\t%s %s %s;%n", 
                        Modifier.toString(method.getModifiers()),
                        method.getReturnType(),
                        method.getName()
                        );
            }
            System.out.println("}");
    
        }
    public static void main(String[] args) {
            try {
                ClassViewer.view("java.lang.reflect.Constructor");
            }catch(ArrayIndexOutOfBoundsException e){
                System.out.println("Array Index Out Of Bounds Exception ");
            }
            catch (ClassNotFoundException e) {
                System.out.println("can not find the class");
            }
        }
    }

运行结果如下：

package java.lang.reflect.Constructor;
    public final class java.lang.reflect.Constructor {
    	private java.lang.Class clazz;
    	private int slot;
    	private [Ljava.lang.Class; parameterTypes;
    	private [Ljava.lang.Class; exceptionTypes;
    	private int modifiers;
    	private transient java.lang.String signature;
    	private transient sun.reflect.generics.repository.ConstructorRepository genericInfo;
    	private [B annotations;
    	private [B parameterAnnotations;
    	private volatile sun.reflect.ConstructorAccessor constructorAccessor;
    	private java.lang.reflect.Constructor root;
    	 java.lang.reflect.Constructor();
    	public boolean equals;
    	public class java.lang.String toString;
    	public int hashCode;
    	public int getModifiers;
    	public class java.lang.String getName;
    	public interface java.lang.annotation.Annotation getAnnotation;
    	public class [Ljava.lang.annotation.Annotation; getDeclaredAnnotations;
    	public class java.lang.Class getDeclaringClass;
    	private interface sun.reflect.generics.factory.GenericsFactory getFactory;
    	 class sun.reflect.generics.repository.ConstructorRepository getGenericInfo;
    	public class [Ljava.lang.Class; getParameterTypes;
    	 class [B getRawAnnotations;
    	public class [Ljava.lang.reflect.TypeVariable; getTypeParameters;
    	public boolean isSynthetic;
    	public transient class java.lang.Object newInstance;
    	public class java.lang.String toGenericString;
    	 class java.lang.reflect.Constructor copy;
    	public class [Ljava.lang.reflect.Type; getGenericParameterTypes;
    	public class [[Ljava.lang.annotation.Annotation; getParameterAnnotations;
    	public int getParameterCount;
    	public boolean isVarArgs;
    	public interface java.lang.reflect.AnnotatedType getAnnotatedReturnType;
    	 class [B getAnnotationBytes;
    	public class [Ljava.lang.Class; getExceptionTypes;
    	public class [Ljava.lang.reflect.Type; getGenericExceptionTypes;
    	 void handleParameterNumberMismatch;
    	 boolean hasGenericInformation;
    	 void specificToGenericStringHeader;
    	 void specificToStringHeader;
    	public interface java.lang.reflect.AnnotatedType getAnnotatedReceiverType;
    	private interface sun.reflect.ConstructorAccessor acquireConstructorAccessor;
    	 interface sun.reflect.ConstructorAccessor getConstructorAccessor;
    	 class [B getRawParameterAnnotations;
    	 class java.lang.String getSignature;
    	 int getSlot;
    	 void setConstructorAccessor;
    }

在次过程中遇到的问题和在stack overflow 我发的帖子和回答如下：

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 The console shows a <code>ArrayIndexOutOfBoundsException</code> when I run this program, it could not find the argument in<code>main()</code>. I really don't know the reason, because I do have the argument<code>String[] args</code> in <code>public static void main(String[] args)</code>: 
 <pre><code><code>package reflect; import java.lang.reflect.Constructor; import java.lang.reflect.Field; import java.lang.reflect.Method; import java.lang.reflect.Modifier; import java.time.chrono.JapaneseChronology; public class ClassViewer { public static void view(String clazName) throws ClassNotFoundException{ Class clz=Class.forName(clazName); Package p=clz.getPackage(); System.out.printf("package %s;%n", clz.getName()); int modifier=clz.getModifiers();//取得类型的修饰常数 System.out.printf("%s %s %s {%n", Modifier.toString(modifier), Modifier.isInterface(modifier) ? "interface" :"class", clz.getName() ); //取得声明的数据成员代表对象 Field[] fields =clz.getDeclaredFields(); for(Field field:fields){ //显示权限修饰 System.out.printf("\t%s %s %s;%n", Modifier.toString(field.getModifiers()), field.getType().getName(), field.getName() ); } //取得声明的创建方法代表对象 Constructor[] constructors=clz.getDeclaredConstructors(); for(Constructor constructor:constructors){ System.out.printf("\t%s %s();%n", Modifier.toString(constructor.getModifiers()), constructor.getName() ); } //取得声明的方法成员代表对象 Method[] methods=clz.getDeclaredMethods(); for(Method method:methods){ System.out.printf("\t%s %s %s;%n", Modifier.toString(method.getModifiers()), method.getReturnType(), method.getName() ); } System.out.println("}"); } public static void main(String[] args) { try { ClassViewer.view(args[0]); }catch(ArrayIndexOutOfBoundsException e){ System.out.println("Array Index Out Of Bounds Exception "); } catch (ClassNotFoundException e) { System.out.println("can not find the class"); } } }</code></code></pre> 
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 <a href="http://stackoverflow.com/questions/tagged/arguments" title="show questions tagged 'arguments'" rel="nofollow">arguments</a> 
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 When you are running the code after compiling it, You have to pass argument which is called<a href="https://docs.oracle.com/javase/tutorial/essential/environment/cmdLineArgs.html" rel="nofollow">command line argument</a>. Suppose you want to pass a String <code>Checking</code> in your code then you have to run file as<code>java ClassViewer Checking</code>. –&nbsp; 
 <a href="http://stackoverflow.com/users/5769497/sanket-makani" title="73 reputation" rel="nofollow">Sanket Makani</a> 
 <a href="http://stackoverflow.com/questions/39187953/could-not-find-the-arguments-of-the-main-method#comment65717036_39187953" rel="nofollow">8 hours ago</a> 
 
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 Did you pass a argument to the program? –&nbsp; 
 <a href="http://stackoverflow.com/users/1080064/tkausl" title="3,371 reputation" rel="nofollow">tkausl</a> 
 <a href="http://stackoverflow.com/questions/39187953/could-not-find-the-arguments-of-the-main-method#comment65717038_39187953" rel="nofollow">8 hours ago</a> 
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 Make sure you pass arguments to<code>view</code>. For testing you could change ` ClassViewer.view(args[0]);` to pass an argument like ` ClassViewer.view(className);` where className is a name of a class. –&nbsp; 
 <a href="http://stackoverflow.com/users/3992939/c0der" title="1,290 reputation" rel="nofollow">c0der</a> 
 <a href="http://stackoverflow.com/questions/39187953/could-not-find-the-arguments-of-the-main-method#comment65718025_39187953" rel="nofollow">6 hours ago</a> 
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 Please translate the comments to English as well. As it is, they are useless for most readers who might want to help you. –&nbsp; 
 <a href="http://stackoverflow.com/users/2564301/rad-lexus" title="12,311 reputation" rel="nofollow">Rad Lexus</a> 
 <a href="http://stackoverflow.com/questions/39187953/could-not-find-the-arguments-of-the-main-method#comment65720072_39187953" rel="nofollow">3 hours ago</a> 
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 c0der is right , i was so careless to ignore that the arguement of the static method view(String className). so when i wanna run the method view . i should pass an argument of String and it means a name of a class. so if i pass a correct meaning name like"java.lang.reflect.Constructor" as the argument of the view , it would be ok .change"ClassViewer.view(args[0]);"like below "ClassViewer.view("java.lang.reflect.Constructor");" it would be ok –&nbsp; 
 <a href="http://stackoverflow.com/users/6755152/qiaopan-ma" title="12 reputation" rel="nofollow">qiaopan Ma</a> 
 <a href="http://stackoverflow.com/questions/39187953/could-not-find-the-arguments-of-the-main-method#comment65723590_39187953" rel="nofollow">1 min ago</a> 
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## 1 Answer ##

[active][] [oldest][] [ votes][votes]

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 As has been noted in the comments appropriately, you must provide command-line arguments. 
 Here is example of that on Linux terminal (Mac also has terminal, and for Windows users there's powershell or CMD ) 
 <pre><code><code>$ ls ClassViewer.java $ javac ClassViewer.java $ java ClassViewer ClassViewer package ClassViewer; public class ClassViewer { public ClassViewer(); public static void view; public static void main; }</code></code></pre> 
 Note that apparently class has to be in the same directory 
 <pre><code><code>$ java ClassViewer /home/xieerqi/bin/java2/soundexClass can not find the class $ # This didn't work, so copy the soudnexClass.class into current directory $ cp /home/xieerqi/bin/java2/soundexClass.class . $ java ClassViewer soundexClass package soundexClass; public class soundexClass { public soundexClass(); public static void getSoundex; public static void main; }</code></code></pre> 
 <hr> 
 This also can be done with IDEs (note , that each IDE has their own way): 
 <ul> 
 <li><a href="http://stackoverflow.com/q/9168759/3701431" rel="nofollow">Netbeans</a></li> 
 <li><a href="http://stackoverflow.com/a/7574571/3701431" rel="nofollow">Eclipse</a></li> 
 <li><a href="https://www2.hawaii.edu/~walbritt/ics211/materials/commandline.htm" rel="nofollow">jGRASP</a></li> 
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