Question

我有以下类，下面列出了数组的静态字段。您能否告诉/解释如何创建构造函数来初始化所有数组并将其传递给public static void BookInfo方法。非常感谢任何帮助！

  public class BookInfo {

    // Global arrays accessible by all methods
public static String[] isbnInfo = {

        "978-0060014018",
        "978-0449221431",
        "978-0545132060",
        "978-0312474881",
        "978-0547745527"

      };


public static String[] bookTitleInfo = {

            "The Greatest Stories",
            "The Novel",
            "Smile",
            "The Bedford Introduction to Drama",
            "AWOL on the Appalachian Trail"

           };

public static String[] authorInfo = {

         "Rick Beyer",
         "James A. Michener",
         "Raina Telgemeier",
         "Lee A. Jacobus",
         "David Miller"

        };

public static String[] publisherInfo = {

            "HerperResource",
            "Fawcett",
            "Graphix",
            "Bedford St. Martins",
            "Mariner Books"

            };

public static String[] dateAddedInfo = {

            "05/18/2003", 
            "07/07/1992", 
            "02/01/2010", 
            "09/05/2008", 
            "11/01/2011"

            };

public static int[] qtyOnHandInfo = {7, 5, 10, 2, 8};

public static double[] wholesaleInfo = {12.91, 7.99, 6.09, 54.99, 10.17};

public static double[] retailInfo = {18.99, 3.84, 4.90, 88.30, 14.95};

public static void BookInfo() {

    System.out.println("             Serendipity Booksellers");
    System.out.println("                Book Information\n");       


    for(int i = 0; i < isbnInfo.length; i++){

        System.out.println("ISBN: " + isbnInfo[i]);
        System.out.println("Title: " + bookTitleInfo[i]);
        System.out.println("Author: " + authorInfo[i]);
        System.out.println("Publisher: " + publisherInfo[i]);
        System.out.println("Date Added: " + dateAddedInfo[i]);
        System.out.println("Quantity-On-Hand: " + qtyOnHandInfo[i]);
        System.out.println("Wholesale Cost: $ " + wholesaleInfo[i]);
        System.out.println("Retail Price: $ " + retailInfo[i]);
        System.out.println();

         }
            }
    }

Answer 1

您要做的是使用static块。在运行任何其他代码之前，初始化static数据。 constructor仅在实例化对象时被调用，并且它们被称为每个时间，该类型的对象也被实例化，static在应用程序运行时被初始化一次。

public static final String[] ISBN_INFO; static { BookInfo.ISBN_INFO = { "978-0060014018", "978-0449221431", "978-0545132060", "978-0312474881", "978-0547745527" }; // do the same thing with the other blocks }

同样制作static变量final也是一个好主意。

Answer 2

可以在声明或静态块中初始化数组，不需要为此使用构造函数。例如：

private static String[] array = {"a", "b", "c"};

或者像这样：

private static String[] array;
static {
    array = new String[] {"a", "b", "c"};
}

实际上，在构造函数中初始化它可能是错误，每次通过调用构造函数创建新实例时都不应更改静态成员。

Answer 3

静态变量在类加载时加载到内存中。那时候他们只有initialized。您不需要在构造函数中初始化它们。

但是，您可以使用static initializer block初始化它们。

private static int[] arr;
static {
    // initialize your arrays here in static initializer block.
     arr = new int[5];
     arr[0] = 5; arr[1] = 10; ... so on
}

在类加载时，

Static initializer块执行一次。它负责初始化类的静态变量。

此外，静态变量在类的所有实例之间共享。因此，您通过一个实例对它们所做的任何更改都将反映在所有实例中。因此，在构造函数中初始化它们没有意义。

如何使用构造函数进行java静态数组初始化？

3 个答案: