Why does not my Array item change in the foreach?

You can not restore the contents of a position in an Array or a collection through foreach . You have to use the classic for for this.

Array , in a simplistic way, is stored in memory as follows:

• Each of the items (values) assigned to Array are stored in memory locations.

  Endereço    Valor
   #00010  "Portugues"
   #00011  "matemática"
   #00013  "história", 
   #00014  "física"
  

• Each position of Array is assigned a memory location that stores not the value itself, but the address where its value was stored.

  Endereço    Valor  indice
   #00001     #00010   [0]
   #00002     #00011   [1]
   #00003     #00012   [2]
   #00004     #00013   [3]
  

What the foreach variable curso receives is the reference (address) where the value corresponding to the index in question is stored and not the position of the Array

When the condition curso.equals(cursoModificar) is true, the variable curso is (referenced) the address # 00010 .

The variable cursoNovo also references a memory location, the one that was assigned to it when the method was called, eg # 00030 .

When you run the curso = cursoNovo; line, curso starts to reference the # 00030 address, the one where the "sciences" string is, however nothing has changed in Array . The position [0] , which is stored at # 00001 , continues to reference the # 00010 address, which continues to save the String " Portuguese".

Confused? Maybe not if you can think of addresses instead of values.

Note: Address values are only indicative.

You are modifying the value of the local variable 'course', just that, so it is not working.

You would have to change the value of the array.

Type like this

for ( int i = 0; i < cursos.length; i++ )
{
    if ( cursos[i] == cursoModificar )
    {
        cursos[i] = cursoNovo;
        return true;
    }
}
return false;

I made this example keeping in mind that 'courses' is an array, if it is a list, just modify the methods.

If courses are an ArrayList try this:

public boolean changeCurso(String cursoModificar, String cursoNovo) {
    for(String curso : cursos) {
        if (curso.equals(cursoModificar)) {
            int index = aluno.cursos.indexOf(curso);
            aluno.cursos.remove(index);
            aluno.cursos.add(index,cursoNovo);
            return true;
    }
}
    return false; }