从数组中删除项目

Question

Just started taking Java 2, and it has been over 6-7 months since I've taken Java 1 and done much programming at all, so please be kind if I did something dumb

The majority of the three classes below are for a previous assignment where you took a listing from the book and had to add a method called getMax() that returns the value of the highest key in the array, or -1 if the array is empty.

This part worked fine.

For the next part(the part I am having trouble with) we had to modify the assignment so that the item with the highest key is not only returned by the method, but also removed from the array.

To do this I tried:

public long removeMax(PrintWriter pw) 
{
    long maxIndex;
    maxIndex = getMax();
    delete(maxIndex);
    return maxIndex;

}

But the maxIndex = getMax(); and delete(maxIndex); are giving me errors and I'm not quite sure why. Although I'm convinced I'm just making a small mistake due to being rusty at programming.

The error it is giving me is actual and formal argument lists differ in length. I tried changing and switching things around but no matter what I did nothing seemed to work.

Below are the Employee, HighArrayObject and Project21Rev(class where getMax and removeMax are) classes in full.

public class Employee
{
    protected int empNo;            // employee number
    protected String ssno;          // social security number
    protected String lastName;     // Last name
    protected String firstName; // First name

    //This constructor initializes the variables

public Employee(int eNo, String ssn, String lName, String fName) 
    // aliases are used in the function header
{
    empNo = eNo;    // the alias is assigned to the actual value
    ssno = ssn;
    lastName = lName;
    firstName = fName;
}

// Make a no argument constructor as well

public Employee() 
{
    empNo = 0;  
    ssno = "";
    lastName = "";
    firstName = "";
}

/** 
    The copy constructor initializes the object 
    as a copy of another Employee object
    @param object2 The object to copy
*/

public Employee(Employee object2)
{
    empNo = object2.empNo;
    ssno = object2.ssno;
    lastName = object2.lastName;
    firstName = object2.firstName;
} 

// The set method sets a value for each field

public void set(int eNo, String ssn, String lName, String fName)
// aliases are used in the function header
{
    empNo = eNo;    // the alias is assigned to the actual value
    ssno = ssn;
    lastName = lName;
    firstName = fName;
}

// the getKey method returns the employee number

public int getKey()
    { return empNo; }

   // the setKey method sets the employee number
   public void setKey(int id)
  { empNo = id; }

// toString method
// returns a string containing the instructor information

public String toString()
{
    // Create a string representing the object.
    String str = "Employee Number: " + empNo +
                     "\nSocial Security Number: " + ssno +
                     "\nLast Name: " + lastName +
                     "\nFirst Name: " + firstName;
// Return the string;
return str;
}
}

Start of next class

import java.io.*;

class HighArrayObject
{
    protected Employee[] emp;
    protected int nElems;

public HighArrayObject(int max) // constructor
{
    emp = new Employee[max];
    nElems = 0;
}

// The createEmployees method creates an Employee object
// for each element of the array

public static void createEmployees(Employee[] emp, int maxsize)
{
    int empNo;
    String ssno;
    String lastName;
    String firstName;

    // Create the employees
    for(int index = 0; index < emp.length; index++)
    {
    // Get the employee data

        emp[index] = new Employee();
    }
}

public boolean find(long searchKey, PrintWriter pw)
{
    System.out.println("Trying to find item with employee number " + searchKey);
    pw.println("Trying to find item with employee number " + searchKey);

    int j;
    for(j=0; j<nElems; j++)
        if(emp[j].empNo == searchKey)       // == ok since empNo is a primative
            break;                          // exit loop before end
        if(j == nElems)                 // gone to end?
            return false;
        else
            return true;                    // no, found it
}  // end find()

public void insert(int eNo, String sNo, String lName, String fName, PrintWriter pw)
{
    System.out.println("Inserting employee with employee number " + eNo);
    pw.println("Inserting employee with employee number " + eNo);


    Employee temp = new Employee();
    temp.empNo = eNo;
    temp.ssno = sNo;
    temp.lastName = lName;
    temp.firstName = fName;
    emp[nElems] = temp;
    nElems++;
}

public boolean delete(long value, PrintWriter pw)
{
    System.out.println("Deleting employee number " + value);
    pw.println("Deleting employee number " + value);

    int j;
    for(j=0; j < nElems; j++)               // look for it
        if(value == emp[j].empNo)
            break;                              // can't find it
        if(j==nElems)
            return false;
        else                                        // found it
        {
            for(int k=j; k<nElems; k++) // move higher ones down
            {
                emp[k]=emp[k+1];                
            }
        nElems--;                               // decrement size
        return true;
    }
} // end delete

public void display(PrintWriter pw)
{
    System.out.println("The array of employees is: ");
    pw.println("The array of employees is: ");

    for(int j=0; j<nElems; j++)
    {
        System.out.println(emp[j].empNo + " " + emp[j].ssno + " "
         + emp[j].lastName + " " + emp[j].firstName);

         pw.println(emp[j].empNo + " " + emp[j].ssno + " "
         + emp[j].lastName + " " + emp[j].firstName);

    }   // end for
} // end delete
} // end HighArrayObject

Start of next class

import java.io.*;

public class Project21Rev extends HighArrayObject       //reference Gaddis p.658
{
    public Project21Rev(int max)        // subclass constructor
{
    super(max);                     // call superclass constructor
}

public void getMax(PrintWriter pw)  // new functionality as required by the assignment
   {
   int maxIndex = -1;  // not found yet

if(nElems == 0)
    System.out.println("Number of elements is 0");
    else
    {
    int max = emp[0].empNo;  // assume the first value is the largest
     maxIndex = 0;

    for (int i = 1; i < nElems; i++)  //now check the rest of the values for largest
    {
        if(emp[i].empNo > max)
        {
           maxIndex = i;
        }
     }
     System.out.println("The largest value is " + emp[maxIndex].empNo + " " + emp[maxIndex].ssno + " " + emp[maxIndex].lastName + " " + emp[maxIndex].firstName);
       pw.println("The largest value is " + emp[maxIndex].empNo + " " + emp[maxIndex].ssno + " " + emp[maxIndex].lastName + " " + emp[maxIndex].firstName);
     System.out.println("at location " + maxIndex);
     pw.println("at location " + maxIndex);
    }
   }

     public long removeMax(PrintWriter pw) 
{
    long maxIndex;
    maxIndex = getMax();
    delete(maxIndex);
    return maxIndex;

}

// modified find method follows   
   public void find( int searchKey, PrintWriter pw)
   { 
  System.out.println("Trying to find item with employee number " + searchKey);
  pw.println("Trying to find item with employee number " + searchKey);

  int j;
  Boolean found = false;
  for(j=0; j < nElems; j++)
     if(emp[j].empNo == searchKey)
     {
        found = true;
        System.out.println("Found " + emp[j].empNo + " " + emp[j].ssno + " " + emp[j].lastName + " " + emp[j].firstName);
        pw.println("Found " + emp[j].empNo + " " + emp[j].ssno + " " + emp[j].lastName + " " + emp[j].firstName);
        System.out.println("at location " + j);
        pw.println("at location " + j);
     }
     if(found == false)
     {
        System.out.println(searchKey + " Not found");
        pw.println(searchKey + " Not found");
     }
}
}

class Project21RevApp
{
   public static void main(String[] args) throws IOException
   {
    // set up printer output file
  PrintWriter pw = new PrintWriter(new BufferedWriter
       (new FileWriter("output21.dat")));

  int maxSize = 100;            // array size
  Project21Rev arr;                // reference to array
  arr = new Project21Rev(maxSize); // create the array

  arr.insert(77,"A","B","C",pw);
    arr.insert(99,"D","E","F",pw);
    arr.insert(44,"G","H","I",pw);
    arr.insert(55,"J","K","L",pw);
    arr.insert(22,"M","N","O",pw);
    arr.insert(88,"P","Q","R",pw);
    arr.insert(11,"S","T","U",pw);
    arr.insert(00,"V","W","X",pw);
    arr.insert(66,"Y","Z","AA",pw);
    arr.insert(33,"BB","CC","DD",pw);

  arr.display(pw);                // display items

  int searchKey = 35;           // search for item
  arr.find(searchKey, pw);              
    searchKey = 22;           // search for item
  arr.find(searchKey, pw);

  arr.delete(00, pw);               // delete 3 items
  arr.delete(55, pw);
  arr.delete(99, pw);

  arr.display(pw);                // display items again

  // new functionality follows  
  arr.getMax(pw); 

    pw.close();

   }  // end main()
}  // end class Project21RevApp

Answer 1

Well, the error message actually tells you exactly what's wrong.

Your method delete() accepts two parameters:

public boolean delete(long value, PrintWriter pw) {
    // ...
}

You are trying to call it with only one:

delete(maxIndex);

To fix the error, pass the right amount and types of parameters.

Answer 2

Hymm there are too many wrong things. Start by learning what a Method is and how you call it. You are trying to call your method

public void getMax(PrintWriter pw){..}

with

maxIndex = getMax();

Now you see when you deffined that method you told it with VOID that it should return nothing. But it requires a PrintWriter Object. You had the right idea when you created your:

public long removeMax(PrintWriter pw) 

you see that method should receive such variable/object and it will be "pw". So the right way to call your method would be

getMax(pw);

and if you want it to return something you really should just read a bit more about java and the way methods work.

The other big problem is that you are talking about a LIST (abstract data type) but in the code I see

protected Employee[] emp;

Witch is not at all a list but just a simple Array . There is a big difference. If the requirements are that you have an actual java/programming list, then there is no such thing in the Program. It's just an Array that looks like a general list of things, but that is called an Array in most programming languages. Perhaps your teacher makes no difference.

This is not a complete solution but there are too many things to fix and the code is too big for whatever it's suppose to do. Don't get stressed, just continue to read about Java from whatever source you got. Keep in mind you are working with Arrays not a lists in that code and you need to learn some basic information about the language.