CODEWITHSUNDEEP
javalistarraylist
joe
joe

Reputation: 1

How to reverse the all element of ArrayList using reverse method?

I have to make a method that can reverse all elements of ArrayList ... For exmaple, if my list have <12 1 34 56 43> elements. then it should reverse the whole list. <43 56 34 1 12>. I've tried this method, but it doesn't work. Here is the method

public void reverse() { 
int size=0;     
for (int i = 0, j = size - 1; i < size && j >= 0; i++, j--)     
{         
int temp = j;         
j = i;         
i = temp;         
}          
}

when I call this method list.revese(). it doesn't reverse the list. Can anyone please help me out!!!

Upvotes: 0

Views: 801

Answers (3)

Yibin Lin
Yibin Lin

Reputation: 721

Your code deals with the index but not the actual element of the index. Also note that if j < i, you are doing the reversing twice, thus there will be no effect.

public void reverse(List<Integer> list) { 
  int size=list.size();     
  for (int i = 0, j = size - 1; i < size && j >= 0 && i <= j; /** i must be smaller. */ i++, j--)     
  {         
    int temp = list.get(j);         
    list.set(j, list.get(i));         
    list.set(i,temp);         
  }          
}

Upvotes: 3

user3928919
user3928919

Reputation:

Initialize 'size' variable to the length of the ArrayList. You are initializing it to 0.

Upvotes: 0

Casey ScriptFu Pharr
Casey ScriptFu Pharr

Reputation: 1670

Use the ArrayList object, and then after building your array you can just run the following to reverse the contents:

Collections.reverse(your ArrayList Here);

Upvotes: 2

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