Populate an object array

Question

I'm currently studying Java and not quite sure how to do this.

At the moment I have an employee class

public class employee {

private int empID;
private String empName;
private String job;

//constructors;

public employee(){
    this.empID = 0;
    this.empName = "";
    this.job = "";
}
public employee(int empID, String empName, String job){
    this.empID = empID;
    this.empName = empName;
    this. job = job;
}

//gets;

public int getEmpID(){
    return this.empID;
}
public String getEmpName(){
    return this.empName;
}
public String getJob(){
    return this.job;
}

//sets;

public void setEmpID(int empID){
    this.empID = empID;
}
public void setEmpName(String empName){
    this.empName = empName;
}
public void setJob(String job){
    this.job = job;
}

}

While in my main I created an object array of type employee with a size of 2 and then just increase the array count while letting the user enter some basic information and then another loop to print all the information entered.

import java.util.Scanner;
public class employeeArray {

public static void p(String s) {System.out.println(s);}

public static void main(String args[]){
    Scanner k = new Scanner(System.in);
    int empID, size=0, x=0;
    String empName;
    String job;
    employee [] employees = new employee[2];

    for(size = 0; size < 2; size++)
    {
        p("Employee "+(size+1));
        p("Please enter employee ID number: ");
        empID = k.nextInt(); k.nextLine();
        p("Please enter your name: ");
        empName = k.nextLine();
        p("Please enter your job role: ");
        job = k.nextLine();

        employees[size] = new employee();

        employees[size].setEmpID(empID);
        employees[size].setEmpName(empName);
        employees[size].setJob(job);


    }

    for(x=0; x<2;x++){
        p("Hello employee: "+employees[x].getEmpName()+" your job role is "+employees[x].getJob()+ 
                " your log in ID is 0800"+employees[x].getEmpID());
    }
}

}

I understand how to populate each instance of the object by input but say i wanted to increase the size from 2 to 20 but already have the first 10 'pre-entered' so then i could display the 10 i currently have but still allowed to enter 10 more.

ps. sorry for my long-winded question, blocks of code and poor/lack of terminology. I'm new to this.

Answer 1

Don't bother using arrays when you need to dynamically resize them unless it's strictly necessary (and even in that case you could just convert through ArrayList.toArray(..)).

Use an ArrayList<Employee> instead thatn an Employee[]. You won't have to worry about the capacity, you won't have to worry about deleting and moving elements. It would also support generic containers.

As a side note: the naming convention of Java suggests to use Capitalized names for classes.

Answer 2

A Java array (with a small "a" -- a [] object) is fixed size when created. So if you create the array with 10 elements it will always have exactly 10 elements (though some of them may not have non-null values). If you need to increase the size of the array beyond it's currently allocated size then good luck!! .... Er, I mean you must allocate a new, larger array and then copy the contents of the smaller array into it.

Copying an array in this fashion is not all that inefficient, but it is awkward and error-prone, so there are several JDK classes (such as java.util.ArrayList) that can hold a variable-length list and manage the ugly stuff for you. (Truth be told, in general these classes keep an internal array and copy it to a larger one when needed, just as you would, so they're no more efficient. But they simplify coding and reduce errors, and that's the important point.)

Answer 3

First of all change the class name to Employee instead of employee. Stick with java naming conventions. Now You should take advantage of java utility classes instead . for Example ArrayList<Employee>. ArrayList implements dynamically resizing array, which lets the user to insert as much amount of data within it without worrying about the current size of the internal array because ArrayList is there to take care of it. But before using ArrayList to store your Employee objects you need to override equals method in Employee because ArrayList internally uses this method to find out the existence of look a like object in some methods. The equals method looks as follows within Employee class:

@Override
public boolean equals(Object anObject) 
{
    if (this == anObject) 
    {
        return true;
    }
    if (anObject instanceof Employee) 
    {
        Employee anotherEmployee = (Employee)anObject;
        if ((this.toString()).equals(anotherEmployee.toString()))
        {
            return true;
        }
        return false;
    }
    return false;
}
@Override
public String toString()//Override it so that it could be easier to compare two objects of Employee using toString()
{
    return empID+","+empName+","+job;
}

Now , You can use ArrayList in following way:

List<Employee> list = new ArrayList<Employee>();
for(size = 0; size < 2; size++)
    {
        p("Employee "+(size+1));
        p("Please enter employee ID number: ");
        empID = k.nextInt(); k.nextLine();
        p("Please enter your name: ");
        empName = k.nextLine();
        p("Please enter your job role: ");
        job = k.nextLine();

        Employee employee = new Employee();

        employee.setEmpID(empID);
        employee.setEmpName(empName);
        employee.setJob(job);
        list.add(employee);
    }

   for(int i = 0 ;i < list.size() ; i++){
    Employee employee = list.get(i);
    p("Hello employee: "+employee.getEmpName()+" your job role is "+employee.getJob()+ 
            " your log in ID is 0800"+employee.getEmpID());
}

Answer 4

According to you comments you actually don't want a dynamic array but one with a fixed size of 20 and 10 entered in it.

Example:

int[] intArray = new int[20];

intArray[0] = 1
intArray[1] = 2
intArray[2] = 3
intArray[3] = 4
intArray[4] = 5
intArray[5] = 6
intArray[6] = 7
intArray[7] = 8
intArray[8] = 9
intArray[9] = 10

//now to fill the rest of the slots.
for(int i = 10; i < intArray.length; i++) {
    intArray[i] = i + 1;
}

However you'll be the one that's responsible for keeping track what is in the array and what is not and you cant add more than 20 items to the array.

Edit: You edited your post. With the above code you could do what you want. If you really want to dynamically increase your array without using an ArrayList you could use System#arrayCopy

http://docs.oracle.com/javase/7/docs/api/java/lang/System.html#arraycopy(java.lang.Object, int, java.lang.Object, int, int)

It lets you copy your existing array to a new (empty) array with the new size.