参数化 static 变量的用法 摘要 class

Question

我正在为我们公司的客户生成报告。

我有一个抽象的 class 有很多 static final int 成员：

public abstract class Customer_ItemIDs {
   public static final int item_001 = 34535;
   public static final int item_002 = 23455;
   public static final int item_003 = 74565;
   public static final int item_004 = 83480;
   ...
   public static final int item_122 = 65487;

}

在我生成报告的 class 中，我像这样使用它们（稍微简化了一点）：

int itemID_004;
itemID_004 = Customer_ItemIDs.item_004;

现在需求发生了变化。

我需要支持另一个具有完全不同 ItemID 的客户，我想将其放入另一个 static class。项目的名称保持不变，只是值不同。

public abstract class CustomerB_ItemIDs {
   public static final int item_001 = 17538;
   public static final int item_002 = 56756;
   public static final int item_003 = 94445;
   public static final int item_004 = 93757;
   ...
   public static final int item_122 = 69483;

}

如何在不更改初始化 itemID 的每一行代码的情况下正确地对其进行参数化？ 我不想像这样初始化 itemID：

int itemID_004;
if (customer == customerA) {
   itemID_004 = CustomerA_itemIDs.item_004;
}
else if (customer == customerB) {
   itemID_004 = CustomerB_itemIDs.item_004;
}

我想尽可能少地改变。

Answer 1

我想你应该试试 Java Reflections: java.lang.reflect

为了不中断现有的类源代码，我将创建一个方法，它将返回HashMap ，所有字段的名称作为key ，其 int 值作为value ，使用提供的 class 名称作为参数：

public static Map<String, Integer> getStaticVariablesValue(Class givenClass) {
    
    Field[] fields = givenClass.getDeclaredFields();
    Map<String, Integer> resultValues = new HashMap<>();
    
    for (int i = 0; i < fields.length; i++)
        if (fields[i].getType() == int.class)
            try {
                resultValues.put(fields[i].getName(), fields[i].getInt(null));
            } catch (IllegalAccessException e) {
                e.printStackTrace(System.out);
            }
            
    return resultValues;
    
}

这是一个简单的示例，它将为您打印所有具有所提供 Class 值的字段：

import java.util.*;
import java.lang.reflect.*;

class Main {
    public static void main(String args[]) {
        
        Map<String, Integer> customer_ItemIDsValues = new HashMap<>();
        Map<String, Integer> customerB_ItemIDsValues = new HashMap<>();

        customer_ItemIDsValues = getStaticVariablesValue(Customer_ItemIDs.class);
        customerB_ItemIDsValues = getStaticVariablesValue(CustomerB_ItemIDs.class);
        
        //Output values to console
        for (Map.Entry<String, Integer> entry : customer_ItemIDsValues.entrySet()) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
            
        for (Map.Entry<String, Integer> entry : customerB_ItemIDsValues.entrySet()) {
            System.out.println(entry.getKey() + " = " + entry.getValue());
        }
    }
    
    public static Map<String, Integer> getStaticVariablesValue(Class givenClass) {
        
        Field[] fields = givenClass.getDeclaredFields();
        Map<String, Integer> resultValues = new HashMap<>();
        
        for (int i = 0; i < fields.length; i++)
            if (fields[i].getType() == int.class)
                try {
                    resultValues.put(fields[i].getName(), fields[i].getInt(null));
                } catch (IllegalAccessException e) {
                    e.printStackTrace(System.out);
                }
                
        return resultValues;
    }

    abstract class CustomerB_ItemIDs {
       public static final int item_001 = 17538;
       public static final int item_002 = 56756;
       public static final int item_003 = 94445;
       public static final int item_004 = 93757;
       public static final int item_122 = 69483;
    }

    class Customer_ItemIDs {
       public static final int item_001 = 34535;
       public static final int item_002 = 23455;
       public static final int item_003 = 74565;
       public static final int item_004 = 83480;
       public static final int item_122 = 65487;
    }
}