Parsing Objects from String in Java

Question

I am trying to write a general method to parse objects from strings. To be clear, I have the following not-so-elegant implementation:

public static Object parseObjectFromString(String s, Class class) throws Exception {
  String className = class.getSimpleName();
  if(className.equals("Integer")) {
    return Integer.parseInt(s);
  }
  else if(className.equals("Float")) {
    return Float.parseFloat(s);
  }
  else if ...

}

Is there a better way to implement this?

Answer 1

Your method can have a single line of code:

public static <T> T parseObjectFromString(String s, Class<T> clazz) throws Exception {
    return clazz.getConstructor(new Class[] {String.class }).newInstance(s);
}

Testing with different classes:

Object obj1 = parseObjectFromString("123", Integer.class);
System.out.println("Obj: " + obj1.toString() + "; type: " + obj1.getClass().getSimpleName());
BigDecimal obj2 = parseObjectFromString("123", BigDecimal.class);
System.out.println("Obj: " + obj2.toString() + "; type: " + obj2.getClass().getSimpleName());
Object obj3 = parseObjectFromString("str", String.class);
System.out.println("Obj: " + obj3.toString() + "; type: " + obj3.getClass().getSimpleName());
Object obj4 = parseObjectFromString("yyyy", SimpleDateFormat.class);
System.out.println("Obj: " + obj4.toString() + "; type: " + obj4.getClass().getSimpleName());

The output:

Obj: 123; type: Integer
Obj: str; type: String
Obj: 123; type: BigDecimal
Obj: java.text.SimpleDateFormat@38d640; type: SimpleDateFormat

Answer 2

I'm not sure what you're trying to do. Here's a few different guesses:

• You want to be able to convert an object to a string, and vice-versa.

You should look into serialization. I use XStream, but writeObject and java.beans.XMLEncoder also works.

• The user enters text, and you want to coerce it to the "right" type, of which there are many.

Usually, this means a problem with the user specification. What are you receiving from the user, and why would it be able to be so many different kinds?

In general, you will want the type to be as broad as possible: use double if it's a number, and String for almost everything else. Then build other things from that variable. But don't pass in the type: usually, the type should be very obvious.