On different interpretations of the for loop

Structure of a loop for(){}in java:

In code:

for(inicialización;condicion;incremento)
{
    //instrucciones
}

1)

The execution of the for control structure begins with the initialization statement . This statement typically performs initialization of a control variable that is often referred to as a sentinel .

two)

Next, the condition whose result has to be a boolean value true or false is checked.

3)

If the condition evaluates to true, the block of statements delimited by the braces is executed, which are only necessary if there is more than one statement.

4)

Then the increment statement is executed and the condition is checked again. So on until the condition is not met.

In your case:

We ask for a digit.

System.out.println("Introduzca los digitos para la sucesion1");

We prepare a for to go through x data:

for(char digito:){
}

In our case, when doing for(char: digit) we are going to read each character that makes up the string that is stored in digit.

There intervenes :these two points indicate what will be the value of the initialization (remember the form of a for).

for(char digito: q.nextLine()){
}

qIt will be our data scanner and it will nextLine()return the entire string read up to the next line, that is:

"Hello I'm Pepe" will be saved completely, unlike using next()that only Saves up to the space "Hello I'm Pepe" -> "Hello".

We continue, now we will apply that saved string toCharArray(), this function converts that string into an array of characters.

for(char digito: q.nextLine().toCharArray()){
}

So we're saying: "For each character contained in the scanner of nextline(), do whatever is between the two braces."

How does the for work without having an incrementer or conditional?: In the for loop, the initialization, the condition and the increment are optional instructions, but this one has an initializer that is an array, which forces the forto go through each one of the letters that make up said array.

Next we add to seq1the character that is in the iteration of the for (I suppose it is an array)

for (char digito : q.nextLine().toCharArray()) {
    seq1.add(digito - '0');
}

Translating the entire for: For each character of the character array obtained from the scanner that asked the user for the digit, add it to the arrayseq1

Now for your question:

Yes and no, after initialization you can add any "conditions", taking into account that you must use logical operators like &&(and)and ||(or)and respecting the basic structure:

for(inicializacion ; aqui || tus && condiciones ; contador){}

As for the actions, they will go in the code block, not in the body of the for, that is:

for(int i=0; i<a || i<b || i>c; i++){
    // AQUI 
    int x = i + 100;
    int z = i x 2;
}

Examples:

for (int i = 1, j = 100; i <= 100 && j > 0; i = i - 1 , j = j-1) {
    System.out.println("Inside For Loop");
}

for( int i = 0 ; i < 100 || otraCondicion() ; i++ ) {
  System.out.printLn("Inside another For Loop");
}

No, what is meant in that for is:

//  Para cada char en el siguiente array de chars.
for (char digito : q.nextLine().toCharArray()) {  
    seq1.add(digito - '0');  //  has lo siguiente.
}

Your digit variable represents each char within the array returned by q.nextLine().toCharArray() , taking them one at a time until it traverses the entire array.

The for loop you write is a special implementation of the for loop included in Java 5, called for-each .

At a high level, the syntax means:

For each variable of type char, which we will call digito, that is included in the array resulting from converting an Stringto array of char: (Logic of the loop)

A small example:

//un array cualquiera
int[] listaDeNumeros = {1, 2, 3, 4};   

System.out.println("For-each");
for (int numero : listaDeNumeros) {
    System.out.println("Numero: " + numero);
}

System.out.println("For tradicional");
for (int i = 0; i < listaDeNumeros.length; i++) {
    System.out.println("Numero: " + listaDeNumeros[i]);
}

The result is:

For-each
Numero: 1
Numero: 2
Numero: 3
Numero: 4
For tradicional
Numero: 1
Numero: 2
Numero: 3
Numero: 4

If you want to know how it works in more depth, I recommend this StackOverflow question in English . As a summary, before Java 5 the implementation of for-each was done like this:

Iterator<Integer> iterador = listaDeNumeros.iterator();
int numero;
while(iterador.hasNext())  {
    numero = iterador.next();
}

You have the advantage that the reference to each item in your collection is already created, but you lose the control variable of the traditional for loop.

Incidentally, the foreach loop can be used with any object that implements the interface Iterable, for example, all objects that are in the java framework java.util.Collections.