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javadata-structuresstacksize
Duwang
Duwang

Reputation: 191

Java stack size does not return the number of items in the stack

I am new to data structures and programming in general, and im learning the concept of a stack by implementing a string reverser. As i wanted to use the stack size as a counter to pop all the items in the stack, i notice that the stack size does not return the number of items in the stack. Example:

    public String reverse(String string) {
    StringBuffer stringBuffer = new StringBuffer();
    //Use a stack to reverse this string.As a stack is a LIFO collection, it goes by last in first out.
   
    Stack<Character> characters = new Stack<>();
    char[] characterArray = string.toCharArray();
    for(char ch : characterArray) {
        characters.push(ch);
    }
    for(int i=0; i < characterArray.length; i++) {
        stringBuffer.append(characters.pop());
    }
    return stringBuffer.toString();
  

}

input " helloworldz" returns "zdlrowolleh" as expected. But when using the stack size as a counter....

    public String reverse(String string) {
    StringBuffer stringBuffer = new StringBuffer();
    Stack<Character> characters = new Stack<>();
    char[] characterArray = string.toCharArray();
    for(char ch : characterArray) {
        characters.push(ch);
    }
    for(int i=0; i < characters.size(); i++) {
        stringBuffer.append(characters.pop());
    }
    return stringBuffer.toString();

}

it returns "zdlrow",

meaning that the stack size did not return the number of items in the stack. Am i missing anything important? any help would be appreciated.

Upvotes: 0

Views: 163

Answers (3)

Musdon
Musdon

Reputation: 9

Java provides the Iterator interface for iterate through complex data structures like stack, map and lists. you might have to refactor your code to use the iterator interface.

Iterator<Character> iterator = stack.iterator();
while(iterator.hasNext()){
sb.append(stack.pop());
}

Upvotes: 1

Kevin Anderson
Kevin Anderson

Reputation: 4592

If you wanted to do a loop conditioned on information from the characters stack itself, the proper choice would be:

    while (!characters.isEmpty()) {
        stringBuffer.append(characters.pop());
    }

Upvotes: 1

Arvind Kumar Avinash
Arvind Kumar Avinash

Reputation: 79035

The size of the stack is decreased by 1 with every pop operation on it and therefore in the following code block,

for(int i=0; i < characters.size(); i++) {
    stringBuffer.append(characters.pop());
}

the loop will be executed for only the half number of times as compared to that in the following code block

for(int i=0; i < characterArray.length; i++) {
    stringBuffer.append(characters.pop());
}

Upvotes: 2

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