CodeGym/Help with Java Tasks/How to check if specificModifier is set in allModifiers ?...

Level 22

Champs-sur-Marne

13.08.2019
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How to check if specificModifier is set in allModifiers ?

Question about the task

Compare modifiers

Java Multithreading, Level 1, Lesson 2

Under discussion

Hello, can you please help me with this ? I'm not sure I understand the logic behind the task.

Implement the logic of the isModifierSet method, which checks whether the passed allModifiers argument has a specific modifier set (specificModifier).

P.S. Before implementing the task, take a look at the Modifier class and the implementation of isPublic, isStatic, and so on.

Requirements:

The isModifierSet method must be static.
The isModifierSet method should return a boolean.
The isModifierSet method must have two int parameters.
The isModifierSet method must return the correct value according to the task conditions (true, if the specified modifier is set in allModifiers; otherwise, false).

package com.codegym.task.task21.task2102; import java.lang.reflect.Method; import java.lang.reflect.Modifier; /* Compare modifiers */ public class Solution { public static void main(String[] args) { int classModifiers = Solution.class.getModifiers(); System.out.println(isModifierSet(classModifiers, Modifier.PUBLIC)); //true System.out.println(isModifierSet(classModifiers, Modifier.STATIC)); //false int methodModifiers = getMainMethod().getModifiers(); System.out.println(isModifierSet(methodModifiers, Modifier.STATIC)); //true } public static boolean isModifierSet(int allModifiers, int specificModifier) { if(Integer.toBinaryString(specificModifier).equals(Integer.toBinaryString(allModifiers))) return true; else return false; } private static Method getMainMethod() { Method[] methods = Solution.class.getDeclaredMethods(); for (Method method : methods) { if (method.getName().equalsIgnoreCase("main")) return method; } return null; } }

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Adrian

Level 27 , Spanish Town, Jamaica

5 February 2021, 16:13

The answer is even simpler than given below I think: if you use the & operator to compare the binary representation of two ints, for example: ((largeInt & specificInt)==specificInt) specificInt will act like a mask, inverting all the other digits(0's and 1's) except for the binary value of specificInt. essentially, the & operator deletes everything else and keeps specific int. Otherwise, you could solve this task by converting the int to a string using the Modifier.toString decoder method

return Modifier.toString(allModifiers).contains(Modifier.toString(specificModifier));

because allModifiers String value would be: "public static" so we can check if it contains the string value of specificModifier

Angus McDonald

Level 5 , Sydney, Australia

Expert

26 June 2020, 09:41

Adding to this to help me process it.. If we have a look at the Modifier class it states that the access modifiers (static vs public vs private...etc) will be represented by an Integer with specific bit positions. The mention of bit positions suggests we should compare bit positions of the resulting Integer.. not the integer itself. The '&' operator is used to compare binary numbers however doesn't produce a "true" / "false" but instead another bit number. That resulting bit number is what we'll then compare against the specificModifier. The & operator looks at each 0 / 1 of the two bit numbers and compares them giving a "1 = true" or "0 = false" result that it records in a new binary number. SO... we need to figure out if the result of comparing the distinct bit positions of the ints passed as arguments equal the specific modifier. i.e. Juanf's code below. (allModifiers&specificModifier) = ?? Then compare that against the specificModifier for our boolean result.

Juanf Software Developer at EPAM

30 October 2019, 19:38

Please, don't ask me to explain why it works, it was just intuition after reading one comment in other question regarding this task :-D

if((allModifiers&specificModifier)==specificModifier){
            return true;
        }else{
            return false;
        }

+15

Fadi Alsaidi

Level 34 , Carrollton, TX, USA

5 July 2020, 18:36

The allModifiers is the sum of all the Modifiers integers. The Modifiers integers is all set to be the exact number at each bit filed or set. here is the full list : ------------------------------------------------------------------------- public static final int ABSTRACT 1024 public static final int FINAL 16 public static final int INTERFACE 512 public static final int NATIVE 256 public static final int PRIVATE 2 public static final int PROTECTED 4 public static final int PUBLIC 1 public static final int STATIC 8 public static final int STRICT 2048 public static final int SYNCHRONIZED 32 public static final int TRANSIENT 128 public static final int VOLATILE 64 ----------------------------------------------------------------------- So you can see the Main method had Modifier PUBLIC and STATIC so that's 1 for PUBLIC+ 8 for STATIC == 9 So our task is to make sure that 9 contains the 8 bit . There are many ways to check, but the logic you used is a very simple an efficient one. When using the "&" bitwise operator you will get 1 if both bits are 1 otherwise you would get 0. So, the number 9 and 8 in bits/binary will have a 1 at the bit of 8 and therefore will result in 1 at the bit 8. The 9 has 1 at bit one so the resulting number from & operator for both is 8 since it's the only bit with both 1. Another example, lets say you have a allModifiers equal to 13 and you wanted to check if it had Specific Modifier 8 if you do the bitwise operator & you will get 8 whcih means yes the allModifier 13 container the bit 8 >>> take a look at the bits graph

Murat Can Akpınar

Level 28 , Essen, Germany

4 August 2020, 22:34

and you dont even need the if statement, instead just write

return (allModifiers&specificModifier)==specificModifier);

Vitali Kalaskou

Level 31 , Novopolotsk, Belarus

12 March 2022, 12:09

Good explanation, I finally understood this task.

jpcouturier

Level 29 , France, France

24 January, 15:09

nice explanation ! ;)

Kotlet

Level 28 , Wroclaw, Poland

13 August 2019, 19:51

I can't really tell how to fix your code but here is mine:

public static boolean isModifierSet(int allModifiers, int specificModifier) {
      if (specificModifier == Modifier.STATIC){
          return Modifier.isStatic(allModifiers);
      }
      if (specificModifier == Modifier.PUBLIC){
          return Modifier.isPublic(allModifiers);
      }
      return false;
  }

It only covers modifiers from the task, so static and public (to cover all this method should be longer). First it checks what kind of modifier is specific modifier. Then it uses method from Modifier Class to checks, whether in all Solution/method modifiers is number representation of this specific modifier.