I an having trouble figuring out where my variables call from or to

Question

can someone explain what variables do what in beginning Java? I am confused about what the variables point to in the bit of code I am doing for my computer class. I am too new to even know what to search for to get the right answer and the book I am using doesn't help explain anything as it names all the variables the same which confuses me on what is called from where. Thank you Chad

Where does the public void setEmpID(int NewID) set this.empID to NewID?

// access modifier is set to public and a class is declared and named Employee
public class Employee  
{   
    private int empID; 
    private String firstName; 
    private String lastName; 
    private double monthlySalary; (Are these to store the variable values from the main method until class creation or are they defining variables in the object that will be created?)

    //Constructor intializes class Employee to create object Employee with instance variables above. Must be same name as class

    **public Employee(int empID, String firstName, String lastName, double newSalary) //(is this the storage until the class is created or the defining of the variables for the object that will be created?)**
    {
        //ensures empID is a positive number before assignment
        if (empID > 0.0) 
            //assigns empID to variable "empID"
            **this.empID = empID; //where does this assign empID? in the new object or in this class temporarily until the object is created?**

        //assigns firstName to variable "firstName"
        this.firstName = firstName; 

        // assigns lastName to variable "lastName"
        this.lastName = lastName;                         

        //ensure monthlySalary is a positive number before assignmentand if 
        //ends constructor
    }

    **//method that sets the empID(where are these set?)**
    public void setEmpID(int newID)
    {
        this.empID = newID;
    }

    //method that sets the firstName
    public void setFirstName(String newFirst)
    {
        this.firstName = newFirst;
    }

     //method that sets the lastName
    public void setLastName(String newLast)
    {
        this.lastName = newLast;
    }

    //method that sets the monthlySalary for the new obj
    public void setMonthlySalary(double newSalary)

    {
        this.monthlySalary = newSalary;
    }

    **//Gets empid from the object and returns empID to the calling method (I think this is right)**
    public int getEmpID()
    {
        return empID;
    }  

    //gets first name from the object and returns first name to the calling method  
    public String getFirstName()
    {
        return firstName;
    }  

    //gets last name from the object and returns last name to the calling method  
    public String getLastName()
    {
        return lastName;
    }  

    //gets monthly salary from the object and returns it to the calling method  
    public double getMonthlySalary()
    {
        return monthlySalary;          
    }

}

Answer 1

If you want to know about variable visibility this might help. SO Question.

As for when variables have the same name see the code below

Example.java

public class Example {
    private int empID = 0; //Creates a global variable

    public Example(int empID) { //Creates a local variable that is 
                                //initiated when contructor is called
        this.empID = empID; //Calls the global variable and sets it
                            //equal to the local variable
        exampleMethod(); //Calls the method below
    }

    private void exampleMethod() {
        empID = 1; //Sets the global variable to = 1
        //This is the same as this.empID = 1;
    }

    public void setEmpID(int newID) {
        empID = newID; //Sets the global variable to = newID
        //This is the same as this.empID = newID;
    }

    public int getEmpID() {
        return empID; //Gets the value of the global variable
                      //empID. Example use below
    }
}

Example2.java

public class Example2 {
    public Example2() {
        Example ex = new Example(1); //Create and initate an Example class
        System.out.println(ex.getEmpID()); //Prints out Example.empID, aka 1
        ex.setEmpID(2);
        System.out.println(ex.getEmpID()); //Prints out Example.empID, aka 2
    }

    public static void main(String[] args) {
        new Example2(); //Creates and initates an Example2 class
    }
}

And as for variable types this short tutorial goes through them. Tutorial