Set field value with reflection

Question

I m working with one project which is not opensource and I need to modify one or more its classes   In one class is following collection   private Map lt Integer  TTP gt  ttp   new HashMap lt  gt        All what I need to do is use reflection and use concurrenthashmap here  I ve tried following code but it doesnt work   Field f     getClass   getDeclaredField  ttp    f setAccessible true   f set null  new ConcurrentHashMap lt  gt

User · Accepted Answer

Hope this is something what you are trying to do :

import java.lang.reflect.Field;
import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

public class Test {

    private Map ttp = new HashMap(); 

    public  void test() {
        Field declaredField =  null;
        try {

            declaredField = Test.class.getDeclaredField("ttp");
            boolean accessible = declaredField.isAccessible();

            declaredField.setAccessible(true);

            ConcurrentHashMap<Object, Object> concHashMap = new ConcurrentHashMap<Object, Object>();
            concHashMap.put("key1", "value1");
            declaredField.set(this, concHashMap);
            Object value = ttp.get("key1");

            System.out.println(value);

            declaredField.setAccessible(accessible);

        } catch (NoSuchFieldException 
                | SecurityException
                | IllegalArgumentException 
                | IllegalAccessException e) {
            e.printStackTrace();
        }

    }

    public static void main(String... args) {
        Test test = new Test();
        test.test(); 
    }
}

It prints :

value1

User · Answer

The method below sets a field on your object even if the field is in a superclass         Sets a field value on a given object        param targetObject the object to set the field value on     param fieldName    exact name of the field     param fieldValue   value to set on the field     return true if the value was successfully set  false otherwise     public static boolean setField Object targetObject  String fieldName  Object fieldValue        Field field      try           field   targetObject getClass   getDeclaredField fieldName         catch  NoSuchFieldException e            field   null            Class superClass   targetObject getClass   getSuperclass        while  field    null  amp  amp  superClass    null            try               field   superClass getDeclaredField fieldName             catch  NoSuchFieldException e                superClass   superClass getSuperclass                        if  field    null            return false            field setAccessible true       try           field set targetObject  fieldValue           return true        catch  IllegalAccessException e            return false

User · Answer

It s worth reading Oracle Java Tutorial - Getting and Setting Field Values  Field set Object object  Object value  sets the field represented by this Field object on the specified object argument to the specified new value   It should be like this  f set objectOfTheClass  new ConcurrentHashMap lt  gt        You can t set any value in null Object If tried then it will result in NullPointerException    Note  Setting a field s value via reflection has a certain amount of performance overhead because various operations must occur such as validating access permissions  From the runtime s point of view  the effects are the same  and the operation is as atomic as if the value was changed in the class code directly

User · Answer

You can try this     Your class instance Publication publication   new Publication       Get class with full path with package name  Class lt   gt  c   Class forName  com example publication models Publication       Get method Method  method   c getDeclaredMethod   setTitle   String class      set value method invoke  publication    Value to want to set here

User · Answer

You can try this   static class Student       private int age      private int number       public Student int age  int number            this age   age          this number   number             public Student             public static void main String   args  throws IllegalAccessException  NoSuchFieldException       Student student1 new Student          Class g student1 getClass        Field  fields student1 getClass   getDeclaredFields        Field age student1 getClass   getDeclaredField  age        age setAccessible true       age setInt student1 13       Field number student1 getClass   getDeclaredField  number        number setAccessible true       number setInt student1 936        for  Field f fields                      f setAccessible true            System out println f getName       f getInt student1

[java] Set field value with reflection

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