Comparing Strings using Arraylist

Question

I need that in the repetition it identifies the same strings, I know that I need to use the . equals(), however, is giving error, as if the variable x is checking more value that exist in Arraylist, but has as a condition that x is smaller than "data.size()" (which is the size of my vector).

public static void main(String args[]) {
        ArrayList<String> dados= new ArrayList<String>();

        //OBS. Primeiramente inserir os dados, futuramente
        //ler arquivos txt
        dados.add("Dado 2");
        dados.add("Dado 1");
        dados.add("Dado 3");
        dados.add("Dado 3");
        dados.add("Dado 3");
        Collections.sort(dados);  
        //while(dados.contains(dados)){
          //  System.out.println("deu certo");
        //}       
        //for (String x : dados){
        //    System.out.println(x);
        //    if (x.contains(x))
       // }     
        int i;
        int contador = 0;
        int x = 0;
        int tamanho = dados.size();
        for (i = 0; i<tamanho; i++){        
            System.out.println(dados.get(i));
                if (x<dados.size() && dados.get(i).equals(dados.get(++x))){
                System.out.println("entrou no contador");
                contador++;
                }              
        } 
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new main().setVisible(true);
            }
        });
    }

Error generated from code:

[ERRO]
run:
Dado 1
Dado 2
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index: 5, Size: 5
Dado 3
entrou no contador
Dado 3
entrou no contador
Dado 3
    at java.util.ArrayList.rangeCheck(ArrayList.java:653)
    at java.util.ArrayList.get(ArrayList.java:429)
    at projetoic.main.main(main.java:118)
C:\Users\lsilv\AppData\Local\NetBeans\Cache\8.2\executor-snippets\run.xml:53: Java returned: 1
FALHA NA CONSTRUÇÃO (tempo total: 5 segundos)

Answer 1

You can use java streams to count this way:

List<String> list = new ArrayList<String>();
list.add("a");
list.add("b");
list.add("c");
list.add("d");
list.add("b");
list.add("c");
list.add("a");
list.add("a");
list.add("a");

Map<String, Long> counted = list.stream()
   .collect(Collectors.groupingBy(e -> e, Collectors.counting()));

The above code streams and groups the same words e -> e and counting the occurrences Collectors.counting(). Thus the resulting map is < Word, Occurrences>

The result is as follows:

{a=4, b=2, c=2, d=1}

See on ideone

As for your code is as already spoken, pay attention to the condition of the loop. (It is i < size)

Answer 2

You are trying to access the index 5 of an array that goes up to 4 (0,1,2,3,4).

Answer 3

1 - The index i goes from 0 to size-1: data[0]=="Given 1"... data[4]="Given 3" (the last Given 3). Therefore the for condition has to be 'i < size'.

2 - The 'x<data.size()' condition is after trying to pick up the value with 'data.get(++x)' so it does not prevent trying to pick up a value already outside the limits of the array.

3 - What answer do you expect? Because arranging the above conditions the output would be 2.

4 - Reinforce the rLinhares comment, do not put a code/error image, but copy and paste the text itself, so that whoever helps you can enjoy the text. For this use the formatting icon for code: the '{}' icon that appears at the top of the box where you type your question/answer here in the stack. Stay like this:

ArrayList<String> dados = new ArrayList<String>();
dados.add("Dado 2");
dados.add("Dado 1");

Answer 4

The problem is here:

dados.get(++x)

++x is different from x++:

• Post Increment (x++): the post-increment happens after the current expression ends. For example: assuming that x = 1, if you do dados.get(x++) you will have the index item 1 and after this item has been returned (or rather, after the whole expression has been finalized), then the x takes an increment and takes the value 2. Briefly, in literal terms what happens is: dados.get(1)

• Preincrement (++x): the preincrement happens before the expression ends. For example: assuming that x = 1, if you do dados.get(++x) first the variable x will receive an increment by changing its value to 2 and only after that the previous expression will continue, causing you to take the index 2 of the list, and not the 1. Briefly, in literal terms what happens is: dados.get(2).

---

That way, even if you do the validation on if, when using the operator as preincrement, you will try to find a non-existent position in your list.

Switch to dados.get(x++) and it will work.