Java将"this"与非静态方法一起使用

Question

我有一个关于将"this"用于带有方法的类的问题。这是我写的一段代码，它给了我一个错误。在使用"this"引用对象时，我对如何使用类非静态类方法感到困惑。有人能帮帮我吗？

更新，这是我所有的代码

public class customer
{
public String name;
public String accountID;
public String address;
public String creditCardNumber;
public String password;
public book[] bookArray;
public int numBooks;
public String toString(){
return "Customer name: " + this.name + " Customer account ID " + this.accountID
+ " Customer address: " + this.address;
}
public String getName(){ //getter method for customer name
return this.name; 
}
public String getAccountID(){ //getter method for cutomer accountID
return this.accountID;
}
public String getAddress(){ //getter method for customer address
return this.address;
}
public String getCreditCardNumber(){ //getter method for customer creditCardNumber
return this.creditCardNumber;
}
public String getPassword(){ //getter method for customer password
return this.password;
}
public void setPassword(String Password){ //setter method for customer password
Password = password;
}
public void setAddress(String Address){ //setter method for customer address
Address = address;
}
public void setCreditCardNumber(String CreditCardNumber){ //setter method for customer creditCardNumber
CreditCardNumber = creditCardNumber;
}
public customer(){ //constructor method for customer class
this.name = name;
this.address = address;
this.accountID = accountID;
bookArray = new book[500];
numBooks = 0;
}
public void addBook(book currentBook){ //addBook method, adds current book to bookArray and adds one to numBooks int
bookArray[numBooks] = currentBook;
numBooks++;
}

}

基本上，我试图让该方法获取当前的book对象，并将其传递给客户类中的addBook方法，然后该方法将该对象添加到数组中。最好的方法是什么？

public class book
{
public String idNumber;
public String title;
public String author;
public String publisher;
public String yearOfPublication;
public int inStock;
public int sold;
public int price;
public String toString(){
return "Book ID Number: " + this.IDNumber+ " Book Title " + this.bookTitle + " Book Author: " + this.bookAuthor //toString method that returns all info for book class
+ " Book Publisher: " + this.bookPublisher + " Year of Publication: " + this.yearOfPublication; 
}
public String getIDNumber(){ //getter method for book idNumber
return this.idNumber;
}
public String getTitle(){ //getter method for book title
return this.title;
}
public String getAuthor(){ //getter method for book author
return this.author;
}
public String getPublisher(){ //getter method for book publisher
return this.publisher;
}
public String getYearOfPublication(){ //getter method for book yearOfPublication
return this.yearOfPublication;
}
public int getBooksInStock(){ //getter method for book inStock
return this.inStock;
}
public int getBooksSold(){ //getter method for book sold
return this.sold;
}
public int getBookPrice(){ //getter method for book price
return this.price;
}
public void bookSales(int numBooksRequested){ //method  records sale of book to customer object
if(inStock == 0){ //checks if book is out if stock, if so prints error message
System.out.println("Error, " + book.getTitle() + " is currently out of stock.");        
}
else if(numBooksRequested > inStock){ //checks if amount of book requsted is greater than whats in stock, if so prints error message
System.out.println("Error, you have requested more copies of " + this.book.getTitle() + " than is currently in stock");
}
else if(numBooksRequested < 0){ //checks if amount requested is less than 0, if so prints error message
System.out.println("Error, invalid amount");
}
else{
for(int i=0; i<numBooksRequested; i++){ //loops through until the total number of the book ordered is passed through the addBook method
customer.addBook(this.book); //if amount requested is valid, utilizes addBook method to add current book object
inStock = inStock - 1;
}
}
}
public book(String IDNumber, String Title, String Author, String Publisher, String YearOfPublication, int Price){
IDNumber = idNumber;
Title = title;
Author = author;
Publisher = publisher;
YearOfPublication = yearOfPublication;
Price = price;
}
public void reStockBook(int bookRestock){
if(bookRestock < 1){
System.out.println("Error, Invalid Number");
}
else{
inStock = inStock + bookRestock;
}
}
}

Answer 1

这取决于bookSales()在哪里。我猜你有这样的东西，但有更多无关的注释：

class Book() {
private final String bookTitle;
private int inStock;
public String getTitle() { return this.bookTitle; }
public int getQuantity() { return this.inStock; }
public void bookSales(int numBooksRequested) { 
if (this.inStock == 0) { 
System.out.println("Error, " + this.book.getTitle() 
+ " is currently out of stock.");           
} else if (numBooksRequested > this.inStock){ 
System.out.println("Error, you have requested more copies of " 
+ this.getTitle() + " than is currently in stock");
} else if (numBooksRequested < 0){ 
System.out.println("Error, invalid amount");
} else {
for (int i = 0; i < numBooksRequested; i++) { 
customer.addBook(this); 
this.inStock = this.inStock - 1;
} // Wouldn't this.inStock -= numBooksRequested make more sense?
}
}
public Book(String title, int quantity) {
// TODO: Check quantity's not negative, throw exception if it is
this.bookTitle = title;
this.inStock = quantity;
}
}

比方说，在另一个班级，你有

Book bible = new Book("The Holy Bible", 70000);
Book bobsRules = new Book("Robert's Rules of Order", 538);

这行调用构造函数，"圣经"被放入bible.bookTitle，70000被放入bible.inStock。对于Robert的秩序规则也是如此。只有那些可能是私人财产。我假设您提供了getter，所以这就是Book类之外用来访问这些属性的东西。

在编写Book构造函数、getter、setter等时，您不知道各种书籍将使用什么标识符。Java语言规范的作者并不希望你这样做。因此，保留了关键字this，在运行时它可能指bible、bobsRules或我们甚至不知道的书。

在Book类之外，可以使用实例标识符。例如：

bible.bookSales(616);
bobsRules.bookSales(197);

在我所写的内容中，customer是未定义的。customer在您的项目中是如何定义的？也许bookSales()应该取一个Customer customer参数。。。

无论如何，bookSales()不必调用this.getTitle()，它可以直接访问this.bookTitle。然而，性能改进实际上微不足道。

混淆的部分原因可能是"this."不是严格要求的。如果您确实将inStock作为Book的属性，那么您可以将其寻址为与"this.inStock"相同的"inStock"。

请注意IDE的语法高亮显示(在我看来，浅色方案的IntelliJ往往比深色方案的IntelJ更可读(。

我在你发布的内容中看到了其他问题，但这些问题与你的问题没有直接关系，所以我不会解决它们。

Answer 2

this用于区分对象本身中的变量和方法，而不是参数或超类变量

public class Example {
private int book;
public void foo1() {
book; // this is the object's book;
this.book; // this is the same as the above
}
public void foo2(int book) {
book; // this is the method parameter book;
this.book; // this is the object's book;
}
}

Answer 3

这用于引用该类/实例中的变量，通常的方法是用于setter即

String info;
public void setInfo(String info)
{
this.info = info;
}

这确保了实例变量info是根据方法中的info设置的，而不仅仅是将传入的变量设置为其自身。

你有book.this.book这是不正确的，因为它之前不能有任何内容，所以应该是this.book。要引用静态变量，不要使用this，而是使用类名。

即this.book(混凝土类(或book.book(静态(