Methods using a object variable as parameter

Defining methods with object variable as parameter

A class in Java is equivalent to a data type
Recall that:

Example of a method with a class variable as parameter:

public class BankAccount { public int accNum; public String name; public double balance; }
public class Class03 { /* ============================================== Method using an object as parameter ============================================== */ public static String convToString( BankAccount x ) { return( "Account number: " + x.accNum + ", Name: " + x.name + ", Balance: " + x.balance); } public static void main(String[] args) { BankAccount stu1, stu2; stu1 = new BankAccount(); // Create one BankAccount object with // 3 data fields: // stu1.studID, stu1.name, stu1.major stu2 = new BankAccount(); // Create another BankAccount object (with // stu2.studID, stu2.name, stu2.major) stu1.accNum = 12345; stu1.name = "Mary"; stu1.balance = 1000.0; stu2.accNum = 23456; stu2.name = "John"; stu2.balance = 1500.0; String s; s = Class03.convToString( stu1 ); System.out.println("BankAccount 1: " + s); s = convToString( stu2 ); // Short hand method name System.out.println("BankAccount 2: " + s); } }

Output:

BankAccount 1: Account number: 12345, Name: Mary, Balance: 1000.0 BankAccount 2: Account number: 23456, Name: John, Balance: 1500.0

Explanation:

The parameter variable BankAccount x specifies that the variable x is a object reference variable (see: click here )
In the method invocations Class03.convToString( stu1 ) (and Class03.convToString( stu2 )), the value stored in the object reference variables stu1 (and stu2) is copied (passed) to the parameter variable BankAccount x:

Therefore:

Because the object reference variable x reference the object reference variable stu1 , the variable name x.accNum, variable name x.name and variable name x.balance will access the same memory locations (or variables) as x.accNum, x.name and x.balance

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Changing the values of a variable inside an object

The following methods deposit(x, amount) and withdraw(x, amount) will add and subtract the amount amount into/from the BankAccount variable x, respectively:

public class Class04 { /* ============================================== convToString(x): return a String containing information of BankAccount x ============================================== */ public static String convToString( BankAccount x ) { return( "Account number: " + x.accNum + ", Name: " + x.name + ", Balance: " + x.balance); } /* ============================================== deposit(x, amount): Add "amount" to x.balance ============================================== */ public static void deposit( BankAccount x, double amount ) { x.balance += amount; // Add "amount" to x.balance } /* ====================================================== withdraw(x, amount): Subtract "amount" from x.balance ====================================================== */ public static void withdraw( BankAccount x, double amount ) { if ( x.balance >= amount ) x.balance -= amount; // Subtract "amount" from x.balance } public static void main(String[] args) { BankAccount stu1; stu1 = new BankAccount(); // Create one BankAccount object with // 3 data fields: // stu1.studID, stu1.name, stu1.major stu1.accNum = 12345; stu1.name = "Mary"; stu1.balance = 1000.0; String x; x = Class04.convToString( stu1 ); System.out.println("BankAccount 1: " + x); Class04.deposit( stu1, 450 ); x = Class04.convToString( stu1 ); System.out.println("After depsoiting $450: " + x); } }

Output:

BankAccount 1: Account number: 12345, Name: Mary, Balance: 1000.0 After depsoiting $450: Account number: 12345, Name: Mary, Balance: 1450.0

Example Program: (Demo above code)
- Prog file: click here
How to run the program:

Wait a minute... I have a better way to organize the methods !

Currently:

We have all the method defined inside the program class Class04

However:

The methods convToString(x) and deposit(x, amount) operate on BankAccount typed variables

Proposal:

It's better to:

put the methods convToString(x) and deposit(x, amount)
inside the BankAccount class !!!!
(Because they perform operations on BankAccount typed variables !!)

Improved organization:

public class BankAccount { public int accNum; public String name; public double balance; /* ============================================== convToString(x): return a String containing information of BankAccount x ============================================== */ public static String convToString( BankAccount x ) { return( "Account number: " + x.accNum + ", Name: " + x.name + ", Balance: " + x.balance); } /* ============================================== deposit(x, amount): Add "amount" to x.balance ============================================== */ public static void deposit( BankAccount x, double amount ) { x.balance += amount; } /* ====================================================== withdraw(x, amount): Subtract "amount" from x.balance ====================================================== */ public static void withdraw( BankAccount x, double amount ) { if ( x.balance >= amount ) x.balance -= amount; // Subtract "amount" from x.balance } }
public class Class05 { public static void main(String[] args) { BankAccount stu1; stu1 = new BankAccount(); // Create one BankAccount object with // 3 data fields: // stu1.studID, stu1.name, stu1.major stu1.accNum = 12345; stu1.name = "Mary"; stu1.balance = 1000.0; String x; x = BankAccount.convToString( stu1 ); System.out.println("BankAccount 1: " + x); BankAccount.deposit( stu1, 450 ); x = BankAccount.convToString( stu1 ); System.out.println("After depsoiting $450: " + x); BankAccount.withdraw( stu1, 100 ); x = BankAccount.convToString( stu1 ); System.out.println("After withdraw $100: " + x); } }

Output:

BankAccount 1: Account number: 12345, Name: Mary, Balance: 1000.0 After depsoiting $450: Account number: 12345, Name: Mary, Balance: 1450.0 After withdraw $100: Account number: 12345, Name: Mary, Balance: 1350.0

Example Program: (Demo above code)
- The new BankAccount.java Prog file: click here
- The Class05.java Prog file: click here
How to run the program: