BankAccount account1 = new BankAccount(...);,this

Transcription

1 1 6 ',,

2 : (.new ) BankAccount account1 = new BankAccount(...); פ, פ,this,, ) \ פ\( פ פ פ 2

3 ) ( " פ : :? public class BankAccount {... private double balance;... 3

4 :),, ( 3 )queries, accessors( ), ( :)observers( פ, ( :)producers( פ ). )immutable( " )commands, transformers, mutators(, : )constructors( : 4

5 - : precondition - " " -.postcondition " " - פ 5

6 )preconditions( -., " : 6

7 )postconditions(..., :?, :?!) ( : 7

8 ? $prev, $ret, $implies ) )x >=0( :) ( x [0,1]( )"M is a diagonal square matrix ( : ', " ) (!,,! 8

9 BankAccount public class BankAccount { public double getbalance() {...; public long getaccountnumber() {...; פ public Customer getowner )( {...; private double balance; private long accountnumber; private Customer owner; field :.getfield() JavaBeans - GUI Builders 9

10 getter/setter?. )private( getter/setter balance :?getter,?setter public void setbalance(double balance) { this.balance = balance;,, 10

11 פ : פ public void deposit(double amount) { balance += amount; /** * Withdraw amount from the account * 0 < amount <= getbalance() getbalance() == $prev(getbalance()) - amount */ public void withdraw(double amount) {?????????????????????????????????????????????????????????????????????????????? balance -= amount; this.balance :' - 11

12 פ : פ public void deposit(double amount) { balance += amount; /** * Withdraw amount from the account * 0 < amount <= getbalance() getbalance() == $prev(getbalance()) - amount */ public void withdraw(double amount) { balance if (amount -= amount; < 0 amount > getbalance()) { System.out.println("Invalid withdrawal amount: "+ amount); return; balance -= amount; : :' 12

13 : : : /** * Makes a transfer of amount from one account to the other 0 < amount <= from.getbalance() to.getbalance() == $prev(to.getbalance()) + amount from.getbalance() == $prev(from.getbalance()) amount */ public static void transfer(double amount, BankAccount from, BankAccount to) { from.withdraw(amount); to.deposit(amount); 13

14 , ( : ) /** * Makes a transfer of amount from the current * account to the other one */ public void transferto(double withdraw amount, BankAccount other) { other.deposit(amount); withdraw(amount); withdraw 14

15 :!... ',null, - :.null :BankAccount!,,, :. ) (?? 15

16 BankAccount /** * Constructs a new account and sets its owner and identifier id > 0 customer!= null getowner() == customer getaccountnumber() == id getbalance() == 0 */ public BankAccount(Customer customer, long id) { accountnumber = id; owner = customer;! new BankAccount - null 16

17 /** * Constructs a new account and sets its owner and identifier id > 0 customer!= null initialbalance >= 0 getowner() == customer getaccountnumber() == id getbalance() == initialbalance */ public BankAccount(Customer customer, long id, double initialbalance) { this(customer, id); balance = initialbalance;. = :. this().! 17

18 עצמים, מחלקות, נראות ומה שביניהם 18

19 CurrentClass public class CurrentClass { public static void mypublicstaticmethod() { System.out.println("In mypublicstaticmethod"); private static void myprivatestaticmethod() { System.out.println("In myprivatestaticmethod"); public void mypublicmethod() { System.out.print("In mypublicmethod >> "); myprivatemethod(); private void myprivatemethod() { System.out.println("In myprivatemethod"); ) ( 19

20 OtherClass public class OtherClass { public static void otherspublicstaticmethod() { System.out.println("In otherspublicstaticmethod"); private static void othersprivatestaticmethod() { System.out.println("In othersprivatestaticmethod"); public void otherspublicmethod() { System.out.print("In otherspublicmethod >> "); othersprivatemethod(); private void othersprivatemethod() { System.out.println("In othersprivatemethod"); 20

21 CurrentClass- main public class CurrentClass { public static void main(string[] args) { CurrentClass.myPublicStaticMethod(); mypublicstaticmethod(); CurrentClass.myPrivateStaticMethod(); CurrentClass.myPublicMethod(); CurrentClass currentclass = new CurrentClass(); currentclass.mypublicmethod(); // Prints: In mypublicmethod >> In myprivatemethod currentclass.myprivatemethod(); // Prints: In myprivatemethod currentclass.mypublicstaticmethod(); //Has a warning, Prints: In mypublicstaticmethod OtherClass.othersPublicStaticMethod(); otherspublicstaticmethod(); OtherClass.othersPrivateStaticMethod(); // Prints: In mypublicstaticmethod // Prints: In mypublicstaticmethod // Prints: In myprivatestaticmethod // Prints: In otherspublicstaticmethod... OtherClass otherclass = new OtherClass(); otherclass.otherspublicmethod(); // Prints: In otherspublicmethod >> In othersprivatemethod otherclass.othersprivatemethod(); 21

22 ) (! mypublicmethod() currentclass.mypublicmethod() = ( = )import, 22

23 Instance vs. Class (static) Fields Instance fields? Class (static) fields???? 0(! 1 )??!? ( ) 23?

24 public class BankAccount { public static final String BANK_NAME = "BNP"; //static constant private static int lastaccountid = 0; //static field private int id; public BankAccount() { id = ++lastaccountid; // unique ID for every account /* static method */ public static void main(string[] args) { System.out.println(lastAccountId); System.out.println(id); BankAccount account = new BankAccount(); System.out.println(account.id); Why?? /* instance method */ public void printstuff() { System.out.println(lastAccountId); System.out.println(id); 24

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