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。
时间: 2024-10-06 04:44:53