从较大的数字中提取一个较小的数字

Question

在这种情况下，我想取一个long UPC //12 digits，提取数字1-6，并将它们存储为private final MANUFACTURER_ID，并将数字7-11存储为private final ITEM_NUMBER。我有一个代码块，它以一种非常丑陋和迂回的方式执行这个任务，我相信有一种更简洁和正确的方法来完成这个任务。

下面是包含UPC变量的InventoryItem类中的相关代码。对于从UPC中提取数字的部分，是否有一种不同的、更简洁的方法来做到这一点？

public InventoryItem(
        long UPC, 
        Category category, 
        Unit_Of_Measure unitOfMeasure, 
        String binLocation, 
        String aisle, 
        String name, 
        String description, 
        short itemsPerUOM,
        int unitsInStock,
        int unitsLastReceived){

    this.UPC = UPC;
    this.category = category;
    this.unitOfMeasure = unitOfMeasure;
    this.binLocation = binLocation;
    this.aisle = aisle;
    this.name = name;
    this.description = description;
    this.itemsPerUOM = itemsPerUOM;
    this.unitsInStock = unitsInStock;
    this.unitsLastReceived = unitsLastReceived;


    /* The code block below parses and extracts digits 1-6 of a UPC which is
     * the unique manufacturer ID. This block also repeats the same process for
     * digits 7-11 which are the manufacturer-specific Item Number. After these
     * steps, the temp Strings are converted to their long integer values and
     * used to initialize MANUFACTURER_ID and ITEM_NUMBER. The 12th digit of a 
     * UPC is used for checksum and thus is ignored for the scope of this program */


    String str = Long.toString(UPC);
    String tempManufacturerID = "";
    String tempItemNumber = "";
    char[] chArr = str.toCharArray();

    //extract the manufacturer ID
    for(int i = 0; i < 6; i++){
        tempManufacturerID += String.valueOf(chArr[i]);
    }

    //extract the manufacturer's item number
    for(int i = 6; i < 11; i++){
        tempItemNumber += String.valueOf(chArr[i]);
    }

    // unbox and assign the extracted data to their respective variables
    MANUFACTURER_ID = Integer.valueOf(tempManufacturerID);
    ITEM_NUMBER = Integer.valueOf(tempItemNumber); 

}

。

。

解决方案

public InventoryItem(
        long UPC, 
        Category category, 
        Unit_Of_Measure unitOfMeasure, 
        String binLocation, 
        String aisle, 
        String name, 
        String description, 
        short itemsPerUOM,
        int unitsInStock,
        int unitsLastReceived){

    this.UPC = UPC;
    this.category = category;
    this.unitOfMeasure = unitOfMeasure;
    this.binLocation = binLocation;
    this.aisle = aisle;
    this.name = name;
    this.description = description;
    this.itemsPerUOM = itemsPerUOM;
    this.unitsInStock = unitsInStock;
    this.unitsLastReceived = unitsLastReceived;
    this.MANUFACTURER_ID = (int)(this.UPC / 1000000); // <--So much nicer!
    this.ITEM_NUMBER = (int)((this.UPC % 1000000) / 10); // <--So much nicer!

}

Answer 1

简单的算术mod / div操作怎么样？

long manufacturerID = (long) UPC / 1000000L;
long itemNumber = (long) (UPC % 100000L) / 10;

简单的算法，没有昂贵的字符串操作，在性能上要好得多。它看起来也优雅得多。

Answer 2

您可以在整数/longs上这样做：

long longcode = 123456789012L;
long firstpart = longcode / 1000000L;
long secondpart = (longcode - 1000000L * firstpart) / 10L;

在字符串上，可以使用substring()获取字符串部件：

String str = Long.toString(UPC);
String tempManufacturerID = str.substring(0,6);
String tempItemNumber = str.substring(6,11);

Answer 3

Java有一个内置的String方法，名为substring。

String c = "abc".substring(2,3); // Output: b