'set' and 'get' methods

the question then is why define a variable private if it is going to be exposed with get and set methods, just define it public!

the alternative is to pass the 'other' object into this class, and have this class interact with the other class through well known interfaces. This way, how the variable is defined and if it is changed later, will not affect the other class.

mchan0 at 2007-6-29 11:59:22 >

for sure that is the case. does one carry it out when using the variable in the same class? I happen to use the methods to get/set the variable even though being in the same class and it is eg an instance variable, one could do direct assignments. there are advantages both ways I suppose. when get/set is used outside of the class, it serves as a warning signal and possible refactor case.

mchan0 at 2007-6-29 11:59:22 >

that is right on both counts. If you had the following:

public class Test {

// define class variables

private String name;

...

public void setName(String s) {

name = s;

}

public String getName() {

return name;

}

then the user would create their own object by instantiating the class (Test t = new Test();). They can then set about "setting" and "getting" using the accessor and mutator methods provided in the class. The variables would be provided by the user i.e.

t.setName("New name");

hope that helps

ML

mlewis7127 at 2007-6-29 11:59:22 >

That's right, all they do is get the value in the variable, no parameters are required.

When you use getters and setters it is easier to track where the variable is being used by tracking where the getter and setter methods are being referenced. It is much harder to search through the code to find out where you are using a certain variable then you are directly accessing the variable.

EsoralTrebor at 2007-6-29 11:59:22 >

What am I missing? When I import the following class into a driver class, my println statement returns "null, 0.0, $0.00, null".

The driver class is after the BankAccount class.

import java.text.NumberFormat;

public class BankAccount {

private NumberFormat fmt = NumberFormat.getCurrencyInstance();

private final double INTEREST_RATE = 0.055; //interset rate is 5.5%

private String name;

private double accountNumber;

private double currentBalance;

private String dateOpened;

public BankAccount(){}

public BankAccount(String name, double accNum, double balance, String date) {

name = name;

accNum = accountNumber;

balance = currentBalance;

date = dateOpened;

}

//--SET METHODS

public void setString(String string) {

name = string;

}

public void setAccountNumber(double number) {

accountNumber = number;

}

public void setCurrentBalance(double balance) {

currentBalance = balance;

}

public void setDateOpened(String date) {

dateOpened = date;

}

//--GET METHODS !!!NO PARAMETERS!!!

public String getString() {

return name;

}

public double getAccountNumber() {

return accountNumber;

}

public double getCurrentBalance() {

return currentBalance;

}

public String getDateOpened() {

return dateOpened;

}

public String toString() {

return (name + "\t" + accountNumber + "\t" + fmt.format(currentBalance) + "\t" + dateOpened);

}

}

import BankAccount;

public class TestBankAccount {

public static void main(String[] args) {

BankAccount acct1 = new BankAccount("Jack Frost", 4567, 123.45, "August 9, 2000");

BankAccount acct2 = new BankAccount();

BankAccount acct3 = new BankAccount();

System.out.println(acct1);

}

}

mts767 at 2007-6-29 11:59:22 >

> the question then is why define a variable private if it is

> going to be exposed with get and set methods, just

> define it public!

(1) Because you might decide not to have a separate variable for each propety. Using private variables and get/set methods allows you to change

public class Foo {

private byte bar1, bar2, bar3, bar4;

// etc.

}

to

public class Foo {

private int barBitfield;

// etc.

}

without breaking any existing code in other classes.

(2) Because you might want your mutator method to have other side effects than just setting the varaible. The setVisible() method in the component classes is a good example.

nerd2004 at 2007-6-29 11:59:22 >

this example is contrived but maybe useful:

in the first two inner classes, changing from byte to Byte changes the signatures.

public class WhyGetSet

{

private class GetSetbyte

{

private byte b1;

public byte getValue()

{

return b1;

}

public void setValue( byte b )

{

b1 = b;

}

}

private class GetSetByte

{

private Byte b1;

public Object getValue()

{

return b1;

}

public void setValue( Object b )

{

b1 = (Byte)b;

}

}

private class NoGetSetCaller

{

private int val;

public NoGetSetCaller()

{

NoGetSet ngs = new NoGetSet( this );

//or

ngs.setValueFor( this );

}

public void setValue( int v )

{

this.val = v;

}

}

private class NoGetSet

{

private byte b1;

private Byte B1;

public NoGetSet( NoGetSetCaller c )

{

setValueFor( c );

}

private void setValueFor( NoGetSetCaller c )

{

int i = (int) b1;

c.setValue( i );

int I = (int) B1.byteValue();

c.setValue( I );

}

}

public WhyGetSet()

{

}

public static void main( String[] args )

{

WhyGetSet wgs = new WhyGetSet();

}

}

mchan0 at 2007-6-29 11:59:22 >

It's also important to note that it is standard to have your getter and setter methods match your private variable name. In your code that you pasted, I notice that you have

public void setString(String string) {

name = string;

}

This method, by the common convention, would be better named as setName, since that is actually what you're setting. Besides that, you have two String properties in your class, name and dateOpened. So how do I know which variable setString is setting?For that matter, I would expect the toString() method to return the same value I passed into setString(), but that is incorrect!

So you see, by keeping with the naming convention you make your classes easier to understand, read, and maintain. In so doing, you make something that is more reliable and reusable in the future.

--David

sage_sam at 2007-7-1 9:07:21 >