Why my code doesn't work for numbers higher than 127 ?

Question about the task

Resolved

Hi, I don't understand why my code doesn't work. I guess it's because I used Integer (which we have to use) but I don't know how to bypass it. I tried to change Integer by Long, but it didn't work. Thanks!

1. Create a list of numbers.
2. Use the keyboard to add 10 numbers to the list.
3. Display the length of the longest sequence of repeating numbers in the list.

Example for the list 2, 4, 4, 4, 8, 8, 4, 12, 12, 14:
3

The value is 3, because the longest sequence of repeating numbers is three fours.

Requirements:

The program must display a number on the screen.
The program should read values from the keyboard.
In the main method, declare an ArrayList variable with Integer elements and immediately initialize it.
The program should add 10 numbers to the collection in accordance with the conditions.
The program should display the length of the longest sequence of repeating numbers in the list.

package com.codegym.task.task08.task0812; import java.io.*; import java.util.ArrayList; /* Longest sequence */ public class Solution { public static void main(String[] args) throws IOException { ArrayList<Integer> list = new ArrayList<Integer>(); BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); for(int i = 0; i < 10; i++){ list.add(Integer.parseInt(reader.readLine())); } int maxLength = 1; for(int i = 0; i < 9; i++){ int maxCurrentNumberLength = 1; if(list.get(i) == list.get(i + 1)){ for(int j = i + 1; j < list.size(); j++){ if(list.get(j) == list.get(i)){ maxCurrentNumberLength ++; } else { break; } } } if(maxCurrentNumberLength > maxLength){ maxLength = maxCurrentNumberLength; } } System.out.println(maxLength); } }

Comments (2)

Popular
New
Old

You must be signed in to leave a comment

Lisa

Level 41

9 February 2022, 10:08

solution

The more interesting question would be why it works till 127. You probably have forgotten that you're working with objects and not primitives and when you compare objects using == you only compare references and not object state. So why are the references the same till 127? That's cause the Integer class (and some more wrapper classes) use some sort of internal caching (interning). As long as you use autoboxing (like Integer i = 1;) or the valueOf() method the class checks if the added number is <128 and if so it refers to a pre created object. So all values up to 127 are linking to the very same object, the references are the same. Btw. the String class has a similar mechanism (string interning).

Integer i1 = 1; // Integer checks if the added value is < 128 and refers to a cached version
Integer i2 = Integer.valueOf(1); // same here
System.out.println(i1 == i2); // proof

Integer i3 = new Integer(1); // this not happens when using the new operator... here a new Object gets created
System.out.println(i1 == i3); // proof

Integer i4 = 128; // if the value is >= 128 a new object gets created, too (no caching)
Integer i5 = 128;
System.out.println(i4 == i5); // proof
System.out.println(i4.equals(i5)); // true

Alexandre Desbois

Level 10 , Chamarandes-Choignes, France

9 February 2022, 13:18

Thanks!