java反射技术代码

下面为java反射技术的一个应用：

下面的代码打印了一个类的全部信息。这个程序将提醒用户输入类名，然后输出类中的所有构造器的签名、方法和所有属性

package myProgram;

import java.util.*;
import java.lang.reflect.*;

/**
 * This program uses reflection to print all features of a class
 * @version 1.1 2004-02-21
 * @author Cay Horstmann
 * Copier **
 * copy time 2012-03-06
 *
 */
public class ReflectionTest {
    public static void main(String[] args){
        //read class name from command line 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 (e.g. java.util.Date):");
            name = in.next();
        }

        try{
            //print class name and surpclass name (if != Object)
            Class c1 = Class.forName(name);
            Class superc1 = c1.getSuperclass();
            String modifiers = Modifier.toString(c1.getModifiers());
            if(modifiers.length() > 0)
                System.out.println(modifiers + " ");
            System.out.println("class "+name);
            if(superc1 != null && superc1 != Object.class)
                System.out.println("extends "+superc1.getName());

            System.out.print("\n{\n");
            printConstructors(c1);
            System.out.println();
            printMethods(c1);
            System.out.println();
            printFields(c1);
            System.out.println("}");
        }catch(ClassNotFoundException e){
            e.printStackTrace();
        }
        System.exit(0);
    }


    /**
     * Print all constructors of a class
     * @param c1 a class
     */
    public static void printConstructors(Class c1){
        Constructor[] constructors = c1.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 c1 a class
     */
    public static void printMethods(Class c1){
        Method[] methods = c1.getDeclaredMethods();

        for(Method m : methods){
            Class retType = m.getReturnType();
            String name = m.getName();

            System.out.println("  ");
            //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.print(paramTypes[j].getName());
            }
            System.out.println(");");
        }
    }

    /**
     * prints all fields of a class
     * @param c1 a class
     */
    public static void printFields(Class c1){
        Field[] fields = c1.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+ ";");
        }
    }

}

结果

Enter class (e.g. java.util.Date):
java.lang.Double (此行为输入的值)
public final
class java.lang.Double
extends java.lang.Number

{
  public java.lang.Double(java.lang.String);
  public java.lang.Double(double);


public int hashCode();

public static native long doubleToRawLongBits(double);

public static long doubleToLongBits(double);

public static native double longBitsToDouble(long);

public boolean equals(java.lang.Object);

public volatile int compareTo(java.lang.Object);

public int compareTo(java.lang.Double);

public static java.lang.String toString(double);

public java.lang.String toString();

public static java.lang.String toHexString(double);

public static int compare(double,double);

public static java.lang.Double valueOf(double);

public static java.lang.Double valueOf(java.lang.String);

public static boolean isNaN(double);

public boolean isNaN();

public byte byteValue();

public double doubleValue();

public float floatValue();

public int intValue();

public boolean isInfinite();

public static boolean isInfinite(double);

public long longValue();

public short shortValue();

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;
}