Fuckery.java

import java.lang.reflect.Field;
import java.lang.reflect.Modifier;
import java.util.Random;

/**
 * General fuckery.
 *
 * @author jezza
 * @date Oct 1, 2015
 */
public class Fuckery {

	private static Field modifiersField;
	private static Field typeField;

	private Fuckery() {
		throw new IllegalStateException("Helper class only!");
	}
	
	/**
     	 * Entry Point to the examples.
     	 * ::Output (One of many)::
     	 * It was true
     	 * It was false
     	 * It was true
     	 * It was true
     	 * It was false
     	 * It was false
     	 * TWO
	 */
	public static void main(final String[] args) throws Exception {
		final RandomBoolean fuckedBoolean = new RandomBoolean();
		override(Boolean.class, "TRUE", fuckedBoolean);
		override(Boolean.class, "FALSE", fuckedBoolean);

		System.out.println("It was " + Boolean.FALSE);
		System.out.println("It was " + Boolean.FALSE);
		System.out.println("It was " + Boolean.FALSE);

		System.out.println("It was " + Boolean.TRUE);
		System.out.println("It was " + Boolean.TRUE);
		System.out.println("It was " + Boolean.TRUE);

		override(Test.class, "ONE", Test.TWO);
		System.out.println(Test.ONE.name());
	}
	
	/**
	 * Used for static fields.
	 *
	 * @param clazz
	 *            - The class the field resides.
	 * @param fieldName
	 *            - The name of the field to find.
	 * @param newValue
	 *            - The value to be injected.
	 * @throws Exception
	 */
	public static void override(final Class<?> clazz, final String fieldName, final Object newValue) throws Exception {
		final Field field = clazz.getDeclaredField(fieldName);
		override(field, null, newValue);
	}

	/**
	 * Used for instance fields.
	 *
	 * @param clazz
	 *            - The class the field resides.
	 * @param fieldName
	 *            - The name of the field to find.
	 * @param instance
	 *            - the instance of the class to change.
	 * @param newValue
	 *            - The value to be injected.
	 * @throws Exception
	 */
	public static void override(final Class<?> clazz, final String fieldName, final Object instance, final Object newValue) throws Exception {
		final Field field = clazz.getDeclaredField(fieldName);
		override(field, instance, newValue);
	}

	/**
	 * Used for instance fields.
	 *
	 * @param field
	 *            - The field to change.
	 * @param newValue
	 *            - The value to be injected.
	 * @throws Exception
	 */
	public static void override(final Field field, final Object newValue) throws Exception {
		override(field, null, newValue);
	}

	/**
	 * Used for instance fields.
	 *
	 * @param field
	 *            - The field to change.
	 * @param instance
	 *            - the instance of the class to change.
	 * @param newValue
	 *            - The value to be injected.
	 * @throws Exception
	 */
	public static void override(final Field field, final Object instance, final Object newValue) throws Exception {
		field.setAccessible(true);

		modifiersField().setInt(field, field.getModifiers() & ~Modifier.FINAL);
		typeField().set(field, newValue.getClass());

		field.set(instance, newValue);
	}

	/**
	 * This retrieves the field containing the modifiers of a field.
	 *
	 * @return The field assocated with the field modifiers.
	 * @throws Exception
	 */
	private static Field modifiersField() throws Exception {
		if (modifiersField == null) {
			modifiersField = Field.class.getDeclaredField("modifiers");
			modifiersField.setAccessible(true);
		}
		return modifiersField;
	}

	/**
	 * This retrieves the field containing the class type of a field.
	 *
	 * @return The field assocated with the class type attached to fields.
	 * @throws Exception
	 */
	private static Field typeField() throws Exception {
		if (typeField == null) {
			typeField = Field.class.getDeclaredField("type");
			typeField.setAccessible(true);
		}
		return typeField;
	}
	
	private enum Test {
		ONE, TWO, THREE;
	}

	public static final class RandomBoolean implements java.io.Serializable, Comparable<Boolean> {
		/** use serialVersionUID from JDK 1.0.2 for interoperability */
		private static final long serialVersionUID = -3665804199014368530L;

		private static final Random random = new Random();

		public RandomBoolean() {
		}

		public boolean booleanValue() {
			return random.nextBoolean();
		}

		@Override
		public String toString() {
			return booleanValue() ? "true" : "false";
		}

		@Override
		public int hashCode() {
			return Boolean.hashCode(booleanValue());
		}

		@Override
		public boolean equals(final Object obj) {
			return booleanValue();
		}

		@Override
		public int compareTo(final Boolean b) {
			return Boolean.compare(booleanValue(), b.booleanValue());
		}
	}
}