对象类和数组 - 为什么它返回“null”？ [java]

我编写了一个小类，它创建一个包含 3 个数组的报表对象。在创建对象时，这些数组用值进行初始化。然而，当我测试该类以查看例如部门数组中的内容时，它会打印出数组元素为空。为什么？

 class  Report
 {
        // declare instance variables (arrays)
        public String[] departments = new String[4] ;
        public double[] grossTotals = new double[4] ;
        public double[] taxTotals = new double[4]  ;


        // constructor
        public Report(){
            // declare, create and initialise all in one statement
            String[] departments = {"Accounting", "Sales", "HR", +
                                              "Administration"} ;
            double[] grossTotals = {0.0, 0.0, 0.0, 0.0} ;
            double[] taxTotals = {0.0, 0.0, 0.0, 0.0} ;

    } // END constructor
 } // class  Report

测试类：

 class TestReport 
 {
        public static void main(String[] args) {
            // create report object
            Report r = new Report();

                for (int i = 0; i <= 3 ; i++ )
                {
                System.out.println(r.departments[i]) ;
                }

        } //end main
 } // end test class

thanks

Baba

让它像这样

public Report(){
            // declare, create and initialise all in one statement
            this.departments = {"Accounting", "Sales", "HR", +
                                              "Administration"} ;
            this.grossTotals = {0.0, 0.0, 0.0, 0.0} ;
            this.taxTotals = {0.0, 0.0, 0.0, 0.0} ;

    } // END constru  

实际上，您正在创建构造函数本地的新数组对象，这些对象在构造函数中进行初始化。

您的类字段将使用上面的代码进行初始化。

如果您没有错误地完成此操作，请参阅此文档，它会更好地阐明您的理解 http://download.oracle.com/javase/tutorial/java/nutsandbolts/variables.html

**

Update

:** 上面的代码会给你非法的表达式开始

这是工作代码

 class  Report
 {
        // declare instance variables (arrays)
        public String[] departments = null;
        public double[] grossTotals = null;
        public double[] taxTotals = null;


        // constructor
        public Report(){
              this.departments = new String[]{"Accounting", "Sales", "HR", "Administration"} ;
         this.grossTotals = new double[]{0.0, 0.0, 0.0, 0.0} ;
         this.taxTotals = new double[]{0.0, 0.0, 0.0, 0.0} ;
    } // END constructor
 }