java.lang.reflection打印一个类的全部信息

package com.ljy.chapter5;

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
import java.util.Scanner;

/**
 * This program uses reflection to print all features of a class.
 * @author LIAO JIANYA
 *
 */

public class ReflectionTest
{
    public static void main(String[] args)
    {
        //read class name from command time args or user input
        String name;
        if(args.length > 0)name = args[0];
        else
        {
            Scanner in = new Scanner(System.in);
            System.out.println("Enter class name (e.g java.util.Date): ");
            name = in.next();
        }
        try
        {
            //print class name and superclass name(if != Object)
            Class cl = Class.forName(name);
            Class supercl = cl.getSuperclass();
            String modifiers = Modifier.toString(cl.getModifiers());
            if(modifiers.length() > 0)
                System.out.print(modifiers + " ");
            System.out.print("class " + name);
            if(supercl != null && supercl != Object.class)
                System.out.print(" extends " + supercl.getName());

            System.out.print("\n{\n");
            printConstructors(cl);
            System.out.println();
            System.out.println("----------------------------------------");
            printMethods(cl);
            System.out.println();
            System.out.println("----------------------------------------");
            printFields(cl);
            System.out.println("}");
        }

        catch (ClassNotFoundException e)
        {
            e.printStackTrace();
        }

        System.exit(0);
    }

    /**
     * Prints all constructor of a class
     * @param cl a class
     */
    public static void printConstructors(Class cl)
    {
        Constructor[] constructors = cl.getDeclaredConstructors();
        for(Constructor c : constructors)
        {
            String name = c.getName();
            System.out.print("    ");
            String modifiers = Modifier.toString(c.getModifiers());
            if(modifiers.length() > 0)
                System.out.print(modifiers + " ");
            System.out.print(name + "(");

            //print parameter types
            Class[] paramTypes = c.getParameterTypes();
            for(int j = 0; j < paramTypes.length; j++)
            {
                if(j > 0)
                    System.out.print(", ");
                System.out.print(paramTypes[j].getName());
            }

            System.out.println(");");

        }

    }
    /**
     * Prints all methods of a class
     * @param cl a class
     */

    public static void printMethods(Class cl)
    {
        Method[] methods = cl.getDeclaredMethods();
        for(Method m : methods)
        {
            Class retType = m.getReturnType();
            String name = m.getName();

            System.out.print("   ");
            //print modifiers, return type and method name
            String modifiers = Modifier.toString(m.getModifiers());
            if(modifiers.length() > 0)
                System.out.print(modifiers + " ");
            System.out.print(retType.getName() + " " + name + "(");

            //print parameter types
            Class[] paramTypes = m.getParameterTypes();
            for(int j = 0; j < paramTypes.length; j++)
            {
                if(j > 0)
                    System.out.print(", ");
                System.out.println(paramTypes[j].getName());
            }
            System.out.println(");");

        }
    }

    /**
     * Prints all fields of a class
     * @param cl a class
     */

    public static void printFields(Class cl)
    {
        Field[] fields = cl.getDeclaredFields();

        for(Field f : fields)
        {
            Class type = f.getType();
            String name = f.getName();
            System.out.print("   ");
            String modifiers = Modifier.toString(f.getModifiers());
            if(modifiers.length() > 0)
                System.out.print(modifiers + " ");
            System.out.println(type.getName() + " " + name + ";");
        }
    }
}

这个程序将提醒用户输入类名，然后输出类中所有的方法和构造器的签名，以及全部域名。

输出结果：

Enter class name (e.g java.util.Date):
java.lang.Double
public final class java.lang.Double extends java.lang.Number
{
    public java.lang.Double(double);
    public java.lang.Double(java.lang.String);

----------------------------------------
   public boolean equals(java.lang.Object
);
   public static java.lang.String toString(double
);
   public java.lang.String toString();
   public int hashCode();
   public static native long doubleToRawLongBits(double
);
   public static long doubleToLongBits(double
);
   public static native double longBitsToDouble(long
);
   public int compareTo(java.lang.Double
);
   public volatile int compareTo(java.lang.Object
);
   public byte byteValue();
   public short shortValue();
   public int intValue();
   public long longValue();
   public float floatValue();
   public double doubleValue();
   public static java.lang.Double valueOf(double
);
   public static java.lang.Double valueOf(java.lang.String
);
   public static java.lang.String toHexString(double
);
   public static int compare(double
, double
);
   public static boolean isNaN(double
);
   public boolean isNaN();
   public static boolean isInfinite(double
);
   public boolean isInfinite();
   public static double parseDouble(java.lang.String
);

----------------------------------------
   public static final double POSITIVE_INFINITY;
   public static final double NEGATIVE_INFINITY;
   public static final double NaN;
   public static final double MAX_VALUE;
   public static final double MIN_NORMAL;
   public static final double MIN_VALUE;
   public static final int MAX_EXPONENT;
   public static final int MIN_EXPONENT;
   public static final int SIZE;
   public static final java.lang.Class TYPE;
   private final double value;
   private static final long serialVersionUID;
}

在java.lang.reflect包中有三个类Field、Method和Constructor分别是用于描述类的域、方法和构造器。

这三个类都有一个叫做getName的方法——用来返回项目的名称;getModifiers的方法——返回一个整型数值，用不同的位开关描述public和static这样的修饰符使用情况。

Field类有一个getType方法——用来返回描述域所属类型的Class对象。

Class类中的getFields、getMethods和getConstructors方法将分别返回类提供的public域、方法和构造数组，其中包括超类的公有成员。

Class类的getDeclareFields、getDeclareMethods和getDeclaredConstructors方法将返回类中声明的全部域、方法和构造器，其中包括私有和受保护成员，但不包括超类的成员。