英文:
An interview question about Java reflection
问题
public class Test {public static void main(String[] arges) throws Exception {IA ia = (IA) createObject(IA.class.getName() + "$getName=Abc");System.out.println(ia.getName()); //output: Abcia = (IA) createObject(IA.class.getName() + "$getName=Bcd");System.out.println(ia.getName()); //output: Bcd}public static Object createObject(String str) throws Exception {String[] parts = str.split("\$");String className = parts[0];String[] methodParts = parts[1].split("=");String methodName = methodParts[0];String returnValue = methodParts[1];Class<?> clazz = Class.forName(className);IA proxy = (IA) java.lang.reflect.Proxy.newProxyInstance(clazz.getClassLoader(),new Class[]{IA.class},(proxyObj, method, args) -> returnValue);return proxy;}interface IA {String getName();}}
英文:
public class Test {// 修改方法createObject内容,实现main里面的两处打印public static void main(String[] arges) throws Exception {IA ia = (IA) createObject(IA.class.getName() + "$getName =Abc");System.out.println(ia.getName()); //output: Abcia = (IA) createObject(IA.class.getName() + "$getName= Bcd");System.out.println(ia.getName()); //output: Bcd}// please coding in createObject for true outputpublic static Object createObject(String str) throws Exception {// your coding}interface IA {String getName();}}
Through Google, I learned about coding through the use of reflection and dynamic proxies. But when I tried coding, I found that I couldn't do it...
答案1
得分: 0
Sure, here's the translated code:
public class Test {public static void main(String[] args) throws Exception {IA ia = (IA) createObject(IA.class.getName() + "$getName =Abc");System.out.println(ia.getName()); //output: Abcia = (IA) createObject(IA.class.getName() + "$getName= Bcd");System.out.println(ia.getName()); //output: Bcd}// please code in createObject for true outputpublic static Object createObject(String str) throws Exception {String[] split = str.split("\$getName\\s?=\\s?");String classname = split[0];String value = split[1];return Proxy.newProxyInstance(Class.forName(classname).getClassLoader(),new Class[] { IA.class },(proxy, method, args) -> {if ("getName".equals(method.getName()))return value;throw new Exception();});}interface IA {String getName();}}
Outputs:
AbcBcd
英文:
What about this?
public class Test {public static void main(String[] arges) throws Exception {IA ia = (IA) createObject(IA.class.getName() + "$getName =Abc");System.out.println(ia.getName()); //output: Abcia = (IA) createObject(IA.class.getName() + "$getName= Bcd");System.out.println(ia.getName()); //output: Bcd}// please coding in createObject for true outputpublic static Object createObject(String str) throws Exception {String[] split = str.split("\$getName\\s?=\\s?");String classname = split[0];String value = split[1];return Proxy.newProxyInstance(Class.forName(classname).getClassLoader(), new Class[] { IA.class },(proxy, method, args) -> {if ("getName".equals(method.getName()))return value;throw new Exception();});}interface IA {String getName();}}
Outputs:
AbcBcd
答案2
得分: 0
Sure, here's the translated code:
public static Object createObject(String str) throws Exception {String value = str.split("=")[1].trim();return (IA) () -> value;}
Reflection isn't necessary since we're only interested in the part after the equal sign.
英文:
I would do it like this:
public static Object createObject(String str) throws Exception {String value = str.split("=")[1].trim();return (IA) () -> value;}
There is not really reflection needed because we only care about the part after the equation mark.
答案3
得分: 0
Here's the translation of the code you provided:
public static Object createObject(String str) throws Exception {final String className = str.substring(0, str.lastIndexOf("$"));final String methodName = str.substring(str.lastIndexOf("$") + 1, str.indexOf("=")).trim();final String value = str.substring(str.indexOf("=") + 1).trim();return Proxy.newProxyInstance(Class.forName(className).getClassLoader(),new Class[] { Class.forName(className) },(proxy, method, methodArgs) -> {if (method.getName().equals(methodName)) {return value;} else {throw new UnsupportedOperationException("Unsupported method: " + method.getName());}});}
英文:
As the class name and method name are provided in the parameter, I made no assumption on the IA interface. Everything is dynamic.
// please coding in createObject for true outputpublic static Object createObject(String str) throws Exception {final String className = str.substring(0, str.lastIndexOf("$"));final String methodName=str.substring(str.lastIndexOf("$")+1,str.indexOf("=")).trim();final String value = str.substring(str.indexOf("=") + 1).trim();return Proxy.newProxyInstance(Class.forName(className).getClassLoader(), new Class[] { Class.forName(className) },(proxy, method, methodArgs) -> {if (method.getName().equals(methodName)) {return value;} else {throw new UnsupportedOperationException("Unsupported method: " + method.getName());}});}
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