得到我的子方法越來越錯誤，我解決不了他們

Question

這裏是主類（我想建立一個程序，以檢查在庫存產品）：

/** 
* Shows various details of an item. 
* 
* @author Brian Clarke 
* @version 28 sept 2017 
*/ 
public class Item { 
    // instance variables 
    private String id; 
    private String descr; 
    private int quantity; 
    private double price; 
    private double discount; 

    /** 
    * Constructor for objects of class Item 
    */ 
    public Item(String id, String descr, int quantity, double price, double discount) { 
    // initialise instance variables 
    id = id; 
    descr = descr; 
    quantity = quantity; 
    price = price; 
    discount = discount; 
    } 

    /** 
    * Get and set methods for variables. 
    * 
    * 
    * 
    */ 
    public String getid(String id) { 
    return id; 
    } 
    public String getdescr(String descr) { 
    return descr; 
    } 
    public int getquantity(int quantity) { 
    return quantity; 
    } 
    public double getprice(double price) { 
    return price; 
    } 
    public double getdiscount(double discount) { 
    return discount; 
    } 
    public void setid(String id) { 
    this.id = id; 
    } 
    public void setdescr(String descr) { 
    this.descr = descr; 
    } 
    public void setquantity(int quantity) { 
    if (quantity < 0) 
     quantity = 0; 
    this.quantity = quantity; 
    } 
    public void setprice(double price) { 
    if (price < 0) 
     price = 0.0; 
    this.price = price; 
    } 
    public void setdiscount(double discount) { 
    if (discount < 0 || discount > 0.8) 
     discount = 0; 
    this.discount = discount; 
    } 
    public String toString() { 
    return "Item1{" + "ID = " + id + ", description = " + descr + ", quantity = " + quantity + ", price = " + price + ", discount = " + discount + '}'; 
    } 
    public double computeCost() { 
    return (quantity * price - quantity * price * discount); // Normal price minus price by the percentage discount should give the correct discounted price 
    } 
} 

這裏是測試類在那裏我得到的最後5行的錯誤，例如，（方法getid在Item類不能被應用到給定的類型，需要：java.lang.String發現：沒有參數的原因：實際的和正式的參數列表的長度不同）。

我不知道如何解決這些問題，並嘗試編輯：

/** 
* Test the class Item 
* The code tests all methods in the class Item 
* @author Brian Clarke 
* @version 28 Sep 2017 
*/ 

public class ItemTest { 
    public static void main(String[] args) { 
    // Create two objects to represent two stock items 
    Item item1 = new Item("ZA423", "Refurbished smartphone", 14, 149.99, 0.3); 
    Item item2 = new Item("BD015", "New 40' TV", 8, 299.99, 0.8); 

    item1.computeCost(); 
    item2.computeCost(); 

    item1.setid("ZA423"); 
    item1.setdescr("Refurbished smarthphone"); 
    item1.setquantity(14); 
    item1.setprice(149.99); 
    item1.setdiscount(0.3); 

    System.out.println(item1.toString()); 

    item2.setid("BD015"); 
    item2.setdescr("New 40' TV"); 
    item2.setquantity(8); 
    item2.setprice(299.99); 
    item2.setdiscount(0.8); 

    System.out.printf("\nItem2 ID is: %s\n", item2.getid()); 
    System.out.printf("\nItem2 Description is: %s\n", item2.getdescr()); 
    System.out.printf("\nQuantity is: %s\n", item2.getquantity()); 
    System.out.printf("\nPrice is: %f\n", item2.getprice()); 
    System.out.printf("\nDiscount is: %f\n", item2.getdiscount()); 
    } 
} 

的代碼是不完整的，但是這是大部分。我搜索了很多，但找不到任何答案。我對Java很新，希望能得到任何幫助。

Answer 1

您錯誤地定義getter方法。在你的實現中，你期望爲每個getter方法傳遞一個參數，這沒有多大意義，因爲getter方法是爲了返回一個值。相反

public String getid(String id) { 
    return id; 
} 

你應該做的：

public String getid() { 
    return id; 
} 

刪除所有來自getter方法的參數，它會工作。

UPDATE：

值得一提的

兩個 三件更多的東西：

構造 Item的

• 類是不正確。像id = id;作業將無法正常工作，你應該做的，而不是this.id = id;（你必須明確地說，在左側的id是類和右側的字段id是作爲構造函數參數傳遞的值）
• 當您使用期望所有領域傳遞，你可以標記所有領域final和刪除setter方法來防止這個類的一個實例，從改變其狀態的構造 - 這是繼
• 考慮使用駝峯一個很好的規則值得符號。如果您的字段名稱爲id，則getter方法應稱爲getId和setter - setId。這是一個在Java程序中廣泛使用的約定。

Answer 2

你不想輸入一個參數給getters方法，因爲你需要讓id沒有將它設置爲一個新值，否則你將得到相同的值，你輸入的值， t輸入，這就是爲什麼你會得到錯誤（缺少參數）。請寫下此代碼，以便您可以獲得之前已設置的數據：

/** 
* Shows various details of an item. 
* 
* @author Brian Clarke 
* @version 28 sept 2017 
*/ 
public class Item { 
    // instance variables 
    private String id; 
    private String descr; 
    private int quantity; 
    private double price; 
    private double discount; 

    /** 
    * Constructor for objects of class Item 
    */ 
    public Item(String id, String descr, int quantity, double price, double discount) { 
     // initialise instance variables 
     id = id; 
     descr = descr; 
     quantity = quantity; 
     price = price; 
     discount = discount; 
    } 

    /** 
    * Get and set methods for variables. 
    * 
    * 
    * 
    */ 
    public String getid() { 
     return id; 
    } 
    public String getdescr() { 
     return descr; 
    } 
    public int getquantity() { 
     return quantity; 
    } 
    public double getprice() { 
     return price; 
    } 
    public double getdiscount() { 
     return discount; 
    } 
    public void setid(String id) { 
     this.id = id; 
    } 
    public void setdescr(String descr) { 
     this.descr = descr; 
    } 
    public void setquantity(int quantity) { 
     if (quantity < 0) 
      quantity = 0; 
     this.quantity = quantity; 
    } 
    public void setprice(double price) { 
     if (price < 0) 
      price = 0.0; 
     this.price = price; 
    } 
    public void setdiscount(double discount) { 
     if (discount < 0 || discount > 0.8) 
      discount = 0; 
     this.discount = discount; 
    } 
    public String toString() { 
     return "Item1{" + "ID = " + id + ", description = " + descr + ", quantity = " + quantity + ", price = " + price + ", discount = " + discount + '}'; 
    } 
    public double computeCost() { 
     return (quantity * price - quantity * price * discount); // Normal price minus price by the percentage discount should give the correct discounted price 
    } 
}