从字符串创建对象

Question

I know if I were in PHP I would be able to create an object as following:

// class Name
$var = "Name";
$my_name = new $var("John", "Doe");

Now, I wanted to adopt similar approach in Java . I have a file which I need to parse and produce objects depending on the line read from the file. For example:

2235:org.powertac.common.TariffSpecification::8::addRate::9
2235:org.powertac.common.Tariff::8::new::8
2235:org.powertac.common.TariffSpecification::10::new::1::PRODUCTION
2236:org.powertac.common.Rate::11::new
2236:org.powertac.common.Rate::11::withValue::0.015
2236:org.powertac.common.Rate::11::setTariffId::10
2236:org.powertac.common.TariffSpecification::10::addRate::11
2236:org.powertac.common.Tariff::10::new::10
2247:org.powertac.common.RandomSeed::12::init::DistributionUtilityService::0::model::-7651755067434358
2257:org.powertac.genco.Genco::13::new::nsp1a::true::true
2258:org.powertac.genco.Genco::13::new::nsp1a
2258:org.powertac.genco.Genco::15::new::nsp1b::true::true

then I should create an object of the type Rate , ( new ), with default values. Therefore, parsing that line would yield me: "org.powertac.common.Rate" ( String ) and I wanted to create a org.powertac.common.Rate object. How could I do it? I know it's a lazy evaluation ... how can I create something similar in Java ?

Answer 1

Use the Java Reflection API:

String className = "org.powertac.common.Rate";
String ctorArg = "8";
Class<Rate> clazz = (Class<Rate>) Class.forName(className);
Constructor<Rate> ctor = clazz.getConstructor(String.class);
Rate rate = ctor.newInstance(ctorArg);

Then, if you want to invoke a method using Reflection:

String methodName = "setTariffId";
String methodArg = "1";
Method setTariffId = clazz.getMethod(methodName, String.class);
setTariffId.invoke(rate, methodArg);

Answer 2

It may be easier to use some preexisting serialization / deserialization solution in Java, but here's something that would work for your String based approach:

Class<?> rateClass = class.getClassLoader().loadClass("org.powertac.common.Rate");
Constructor<?> constructor = rateClass.getConstructor(String.class);

Rate rate = (Rate)constructor.newInstance("Value")

So in this case:

2258:org.powertac.genco.Genco::15::new::nsp1b::true::true

you would do the following:

String className = "org.powertac.genco.Genco";
Object[] args = {"nsp1b", true, true};

Class<?> rateClass = getClass().getClassLoader().loadClass(className);
Constructor<?> constructor = rateClass.getConstructor(String.class, boolean.class, boolean.class);

Object deseraliazed = constructor.newInstance(args);

You may want to store the type along with the constructor values.