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。