返回布尔值/从数组中删除该元素的类 [JAVA]

Question

For a class project, I'm supposed to make a Gradebook with the four classes: Main (which just runs the gradebook), Gradebook (which has all the methods I will be using such as add student, remove student, add assignment, etc.), Student (which will maintain the student's name, number, email), and Assignment (which holds all the assignment details). My instructor wrote most of the code design and he left us to write helper methods that find particular students and assignments and return a boolean. I need these helper methods but I don't know how to write it so that I could use the student or assignment they had found (ie how do I remove a student after the helper method had found said student?). All my students and assignments are in separate arrays (not array lists or anything else, per his instructions) and if there's another way without having the return types as booleans, I think I'm able to change the return types as well.

Here's my helper method:

   private boolean findStd (String stdName)
   {
       boolean thing = false;

       for(int i = 0; i < students.length; i++)
       {
           if(stdName.equalsIgnoreCase(students[i].studentName))
           {
               thing = true;
           }
       }

       return thing;
   }        

Here's my removeStudent method for now:

 private boolean removeStudent()
   {
       String name = JOptionPane.showInputDialog("What's the student's name (last, first)?");
       findStd(name);

       return false;
   }             // delete student from list 

Answer 1

Assuming the Student name is stored as "last, first", then you just need to iterate through the array, and delete it once you hit the correct student:

for (int i = 0; i < students.length; i++) {
    if (students[i].studentName.equalsIgnoreCase(name)) {
        // delete student, e.g. students[i] = null;
    }
}

where name is the result from the JOptionPane.

Answer 2

Your logic for finding and removing seems to be off. In order to remove a student from an array you'd like for a couple things to happen

1. I determine if the name of that person I am trying to remove exists.
2. If it does exist in my array then I will remove the student by telling it what name or index to use. (this is where you use the show input dialog)

Try this:

//Change the method for find to return the index, but returns -1
// if the name isn't found which can be used to let a caller of 
// the function know that it does not exist as I will show in the removeStudent()
private int findStd (String stdName)
{
    int indexOfStudent = -1;

    for(int i = 0; i < students.length; i++)
    {
        if(stdName.equalsIgnoreCase(students[i].studentName))
        {
           indexOfStudent = i;
           break;
        }
    }
   //now we will either return a valid index or -1
   return indexOfStudent;
}

private boolean removeStudent()
{
    String name = JOptionPane.showInputDialog("What's the student's name (last, first)?");
    //if the name exists then our findStd() will give us the index
    int indexToRemove = findStd(name);
    if(indexToRemove != -1)
    {
        students[indexToRemove] = null;
        return true;
    }
    return false;
}

Answer 3

There are different ways to "remove" an element from an array. It depends on what you mean by "remove".

1. You can assign null to the array at the position of the element you want to remove.

   Problem: you now have null values in the array, and the rest of your code has to deal with that.

2. You can use a loop (or a utility method) to copy elements left to fill in the "hole" left by the removed element.

   Problem: now you have a "hole" (ie nulls) at the right-hand end. Your code needs to deal with the fact that your conceptual array is smaller than the actual array length; eg

   for(int i = 0; i < students.length /** <<== wrong */ ; i++)

3. You can create a new array with the correct size and copy the elements to it ... using one or two loops, or calls to utility methods.

   Problem: you now need to update all places where you have a reference to the original array.

4. You can use a List rather than an array. The List API provides operations for removing elements.

   Problem: You may not be able to change the declaration of students .

There should be enough information in the above descriptions to tell you what your code needs to do ... in each case.