CODEWITHSUNDEEP
java
Yohombu
Yohombu

Reputation: 31

Why is this Java variable assignment illegal?

Here is the code

import java.util.*;
 class Example
 {
  public static void main(String args[])
  {
    final int x=127; int y=100;
    byte b;
    b=x; //Legal ?
    b=y; //Illegal 
  }
 }

Can you explain why b=y is illegal? I think final means no further change, is that correct?

Upvotes: 1

Views: 354

Answers (1)

Jordan
Jordan

Reputation: 2283

The final keyword does mean "no further change", so you're correct there. The issue here has to do with data "width".

An int can hold more data than a byte (i.e. it is "wider" than a byte). This means that when you do b = x, you're "narrowing" the width of the int to fit into the byte. This only works if the compiler can guarantee that the int is small enough to fit into the byte, which requires the int to be <= 127, and to also be final (so that it cannot later be changed to be > 127).

In your code, both x and y are narrow enough to fit into a byte, but only x is final, so it's the only one the compiler allows to be directly assigned to a byte variable.

  final int x=127; final int y=100; // Made y final
  byte b;
  b=x; //Legal
  b=y; //Also legal 

  final int x=200; final int y=100; // Made x too big
  byte b;
  b=x; //Illegal
  b=y; //Legal

Upvotes: 9

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