Day 9 (this keyword and experiment)

this: Represents the current object or the object currently being created , This class attribute can be called , Call this class method or constructor .

In the method of a class , You can use this. Property name or this. Method To call the properties and methods of the current object , Usually omitted , When the formal parameter name of a method in a class has the same name as the attribute name , You have to use this. Attribute name to operate .（ The constructor of class is similar ）

1、 Call this class property

public class BookTest {
    public static void main(String[] args) {
        Book book = new Book();
        book.setBookName("The Ordinary World");
        book.setBookPrice(66);
        System.out.println(book.getBookName());
        System.out.println(book.getBookPrice());
    }
}

class Book{
    private String bookName;
    private int bookPrice;
    // The method parameter name is the same as the attribute name in the class 
    public void setBookName(String bookName){ 
        // utilize this. Attribute name 
        this.bookName = bookName;
    }
    public String getBookName(){
        return this.bookName;
    }
    public void setBookPrice(int bookPrice){
        this.bookPrice = bookPrice;
    }
    public int getBookPrice(){
        return this.bookPrice;
    }
}

2、 Invoking Constructors

        （1） Inside the constructor of the class , By using this( Parameter list ) To call other constructors of the current class

        （2） Cannot be used inside the constructor this To call yourself , And there can only be one at most this Call statement

        （3） Use this( Parameter list ) The call constructor statement must be placed on the first line of the constructor method

public class BookTest {
    public static void main(String[] args) {
        Book book = new Book("The Ordinary World",66);
        System.out.println(book.info());
    }
}

class Book{
    private String bookName;
    private int bookPrice;
    public Book(){
        System.out.println(" Parameterless constructors ");
    }

    public Book(String bookName){
        this();
        this.bookName = bookName;
    }
    public Book(String bookName,int bookPrice){
        this(bookName);
        this.bookPrice = bookPrice;
    }
    public String info(){
        return "the name of the book is:" + this.bookName + ", the price of the book is:" + this.bookPrice;
    }
}

3、 experiment

Experiment 1 ：

         establish Boy and Girl Two classes , And create private properties name、age, And declare set/get Methods and corresponding constructors ,marry、shout、compare For the methods in their respective classes .（- Express private,+ Express public） 

//Boy.java The code is as follows ：

public class Boy{
    private String name;
    private int age;
// Declare a two parameter constructor 
    public Boy(String name, int age) {
        this.name = name;
        this.age = age;
    }
// Statement set get Method 
    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public int getAge() {
        return age;
    }
// Statement marry Method 
    public void marry(Girl girl){
        System.out.println("marry:"+girl.getName());
    }
    // Statement shout Method 
    public void shout(){
        if(this.age >= 22){
            System.out.println("you can marry");
        }else{
            System.out.println("you're too young to marry");
        }
    }
}

//Girl.java The code is as follows ：

public class Girl {
    private String name;
    private int age;

    public Girl(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
    public void marry(Boy boy){
        System.out.println("marry to:"+boy.getName());
        boy.marry(this); //this： Who is calling marry Method who is the current object 
    }
    // Compare   The current object   And   The object passed in   Age of 
    public int compare(Girl girl){
        return this.age-girl.age;
    }
}

//main()  The code is as follows ：

public class BoyGirlTest{
    public static void main(String[] args) {
        Boy boy = new Boy("Mike",22);//Boy Class instantiation 
        boy.shout();// call Boy Class method 
        Girl girl = new Girl("Marry",20);//Girl Class instantiation 
        girl.marry(boy);// call Girl Class method 
        Girl girl1 = new Girl("Lily",24);
        int result = girl.compare(girl1);// Compare girl And girl1 In the age of  girl call （ For the current object ）
        if (result > 0){
            System.out.println(girl.getName()+" older ");
        }else if (result < 0){
            System.out.println(girl1.getName()+" older ");
        }else{
            System.out.println(girl.getName()+" and "+girl1.getName()+" The same age ");
        }
    }
}

Experiment two ：

        establish Customer Classes and Account class , And realize the function of deposit and withdrawal , And display customer account information .

                （1）Customer The class code is as follows ：

public class Customer {
    private String firstName;
    private String lastName;
    private Account account;
// Declare a two parameter constructor 
    public Customer(String f, String l) {
        firstName = f;
        lastName = l;
    }
// Statement related set get Method 
    public String getFirstName() {
        return firstName;
    }
    public String getLastName() {
        return lastName;
    }
    public void setAccount(Account account) {
        this.account = account;
    }
    public Account getAccount() {
        return account;
    }
}

                （2）Account The class code is as follows ：

public class Account {
    private int id;
    private double balance;
    private double annualInterestRate;
// Declare a three parameter constructor 
    public Account(int id, double balance, double annualInterestRate) {
        this.id = id;  // user id
        this.balance = balance;  // User balance 
        this.annualInterestRate = annualInterestRate;  // Annual interest rate 
    }
// Declare properties related set  get Method 
    public void setId(int id) {
        this.id = id;
    }

    public void setAnnualInterestRate(double annualInterestRate) {
        this.annualInterestRate = annualInterestRate;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }

    public int getId() {
        return id;
    }

    public double getAnnualInterestRate() {
        return annualInterestRate;
    }

    public double getBalance() {
        return balance;
    }
    // Declare the method of withdrawal 
    public void withdraw(double amount){
        if(this.balance < amount){
            System.out.println(" Lack of balance , Withdrawal failed ");
        }else{
            this.balance -= amount;
            System.out.println(" Successfully deposited :"+amount);
        }
    }
    // State how to save money 
    public void deposit(double amount){
        if (amount > 0) {
            this.balance += amount;
            System.out.println(" Successfully removed :"+amount);
        }
    }
}

                （3） A functional test  

public class AccountCustomerTest {
    public static void main(String[] args) {
        //Customer Class instantiation 
        Customer c1 = new Customer("Jane","Smith");
        //Account Class instantiation 
        Account a1 = new Account(1000,2000,0.0123);
        // Put the object c1 The account object of is set as object a1  （ Connect the two classes ）
        c1.setAccount(a1);
        // adopt getAccount Method calls the save method 
        c1.getAccount().deposit(100);
        // Call the withdrawal method 
        c1.getAccount().withdraw(960);
        c1.getAccount().withdraw(2000);
        // Print customer account information 
        System.out.println("Customer ["+c1.getLastName()+","+c1.getFirstName()+" has a account: id is "+a1.getId()
                +", annualInterestRate is "+ a1.getAnnualInterestRate()*100 +"%, balance is "+a1.getBalance());
    }
}

                 Output ： 

  Experiment three ：

         establish Customer1、Account1、Bank Classes and related methods , And write BankTest Test related functions

                （1）Customer1 The class code is as follows ：

public class Customer1 {
    private String firstName1;
    private String lastName1;
    private Account1 account1;

    public Customer1(String f,String l) {
        this.firstName1 = f;
        this.lastName1 = l;
    }

    public String getFirstName1() {
        return firstName1;
    }

    public String getLastName1() {
        return lastName1;
    }

    public void setAccount1(Account1 account1) {
        this.account1 = account1;
    }
    public Account1 getAccount1() {
        return account1;
    }
}

                （2）Account1 The code is as follows ：

public class Account1 {
    private double balance;

    public Account1(double init_balance) {

        this.balance = init_balance;
    }

    public double getBalance() {
        return balance;
    }

    public void withdraw(double amt) {
        if (this.balance < amt) {
            System.out.println(" Lack of balance , Withdrawal failed ");
        } else {
            this.balance += amt;
            System.out.println(" Successful withdrawals ：" + amt + ", The current balance is : " + this.balance);
        }
    }

    public void deposit(double amount) {
        if (amount > 0) {
            this.balance += amount;
            System.out.println(" Deposit success ：" + amount + ", The current balance is : " + this.balance);
        } else {
            return;
        }
    }
}

                （3）Bank The class code is as follows ：

public class Bank {
    // Create private  Customer1 An array of objects    Store multiple customers 
    private Customer1[] customers = new Customer1[10];   //10*3
    private int NumberOfCustomer;
    // Create a parameterless constructor 
    public Bank(){
    }

    public void addCustomer(String f,String l){
        // Create a new Customer object   And call the constructor to assign the initial value 
        Customer1 c1 = new Customer1(f,l);
        //customerIndex: Index in the object array where the customer is located 
        int customerIndex = this.NumberOfCustomer++;
        // Will create a new object c1 Put it into the object array 
        this.customers[customerIndex] = c1;
    }
    public int getNumberOfCustomers(){
        return this.NumberOfCustomer;
    }
    // Return value as object 
    public Customer1 getCustomer(int index){
        // If the index meets the condition 
        if (index >= 0 && index < this.NumberOfCustomer){
            // return index Where you are 
            return this.customers[index];
        }else{
            return null;
        }
    }
}

                （4）BankTest test

public class BankTest {
    public static void main(String[] args) {
        //Bank Instantiation 
        Bank bank = new Bank();
        // Add customers 
        bank.addCustomer("Zhang","GuoHua");
        // Create customer 
        bank.getCustomer(0).setAccount1(new Account1(2000));
        // Withdraw money 
        bank.getCustomer(0).getAccount1().withdraw(500);
        // Deposit money 
        bank.getCustomer(0).getAccount1().deposit(10000);
        bank.getCustomer(0).getAccount1().withdraw(20000);
        // Get the specified customer balance information 
        double theRest= bank.getCustomer(0).getAccount1().getBalance();
        System.out.println(" Customer "+bank.getCustomer(0).getLastName1()+" The balance of is : "+theRest);
        System.out.println("-----------------------------------");
        bank.addCustomer("DaHua","OuYang");
        // Get the current number of customers 
        System.out.println(" The current number of bank customers is : "+bank.getNumberOfCustomers());
    }
}