Java Code House

In our vlast posts we only concentrated on sniffing class declaration and its members. But this time we will go beyond it and try to get and set field values of a given class using Java Reflection.For this we just need an instance of a class. Though here we will deal with public fields only and someone might think that we can get and set field values in thes cases directly using instance of that class. But this is not the actual case in real situation. This is done only in places where directly we cannot set thopse values as in case of private members. So here we have used method getDeclaredField() (we will deal with private members later). Here we will just show that once you have the class refernce and the instance of a particualr class you can get and set the field values whether its an integer,float,string or array. There are seperate methods for different primitive data types like getInt() and setInt() for int , getLong() and setLong() for long and so on. But for data types other than primiotive ones you have to use get() and set() methods.
      Here in our demo we jave created a class Person with fields of type int, String and a String array. So you will be able to uinderstand clearly how to use different methods depending on data type.
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import java.lang.reflect.Field;
import java.util.Arrays;

import static java.lang.System.out;

class Person{
public int id=1521;
public String name="Luther";
public String hobbies[]={"cricket","music"};
}

public class FieldChanger {
public static void main(String[] args) {
try{
    Class c=Person.class;  //getting class reference
    Person pobj=new Person();
    
    Field id=c.getDeclaredField("id");  //getting field reference
    out.println("BEFORE :   id = "+id.getInt(pobj));  //getting initial int value
    id.setInt(pobj, 1926);  //setting a new int value
    out.println(" AFTER :   id = "+id.getInt(pobj));
    
    Field name=c.getDeclaredField("name");
    out.println("BEFORE :   name = "+name.get(pobj));  //getting initial String value
    name.set(pobj, "Jennifer");  //setting a new String value
    out.println(" AFTER :   name = "+name.get(pobj));
    
    Field hobbies=c.getDeclaredField("hobbies");
    //showing initial array values
    out.println("BEFORE :   hobbies = "+Arrays.asList(pobj.hobbies));
    String[] nhob={"football"};
    hobbies.set(pobj, nhob);  //setting new values for array
    out.println(" AFTER :   hobbies = "+Arrays.asList(pobj.hobbies));
    
}catch(NoSuchFieldException|
IllegalAccessException e){ }
}
}