Java 变量未设置

Question

好吧，所以我试图让变量“totalTax”和“total”保存商品的价格，当我在设置它们的方法中调用它们时，它们工作得很好，但是当我从另一个类，它返回0。

public class Input
{
private Scanner keybd;
private String[] costArray;
private String[] itemArray;
private double totalTax;
private double total;

/**
 * Constructor for objects of class Scanner
 * 
 * @param anyAmountofItems the amount of items you are going to be buying
 */
public Input(int anyAmountofItems)
{
    keybd = new Scanner(System.in);
    costArray = new String[anyAmountofItems];
    itemArray = new String[anyAmountofItems];
    totalTax = 0.0;
    total = 0.0;
}
/**
 * Mutator method to set the item names and costs
 * 
 * @param anyValue the tax rate percentage (ex. 0.08 for 8%)
 */
public void setArray(double anyValue){
    //System.out.println("Enter the sales tax percentage: ");
    //double salesTax = keybd.nextDouble();
    //for(int index=0; index < itemArray.length; index++){ 
    //System.out.println("Enter the item name: ");
    //itemArray[index] = keybd.next();}
    double totalTax=0.0;
    double total=0.0;
    for(int indexc=0; indexc < costArray.length; indexc++){
       System.out.println("Enter the item name: ");
       String anyName = keybd.next();
       itemArray[indexc] = anyName;
       System.out.println("Enter the item cost: ");
       double cost = Double.valueOf(keybd.next()).doubleValue();
       costArray[indexc] = " " + cost;
       totalTax = totalTax + (cost * anyValue);
       total = total + cost;
    }
    //for(int indexa=0; indexa < itemArray.length; indexa++){
    //System.out.println(itemArray[indexa] + "-" + costArray[indexa]);}
    //System.out.println("Sales Receipt");
    //System.out.println("--------------");
    //for(int i=0;i<costArray.length;i++){
    //    System.out.println(itemArray[i] + " - $" + costArray[i]);
    //}
    //returnCostArray();
    //System.out.println("Total tax: $" + totalTax);
    //System.out.println("Total cost pre-tax: $" + total);
    //System.out.println("Total cost including tax: $" + (total+totalTax));
    totalTax = totalTax;
    total = total;
}
public String returnArray(int anyElement){
    int index = anyElement - 1;
    return itemArray[index];
}
public double returnTotal(){
    return total;
}
public double returnTotalTax(){
    return totalTax;
}
public void returnCostArray(){
for(int i=0;i<costArray.length;i++){
    System.out.println(itemArray[i] + " - $" + costArray[i]);
    }
 }
 }

然后，我运行这个使用 Input 类的类，它返回 0，但是当我在已有的类中执行 System.out.println 时，它会工作并返回总数。

public class TaxClass
{
private Input newList;
/**
 * Constructor for objects of class Tax
 * 
 * @param anyAmount Enter the number of items
 */
public TaxClass(int anyAmount)
{
    newList = new Input(anyAmount);
}
/**
 * Mutator method to add items and their cost
 * 
 * 
 * @param anyTax Enter the sales tax percentage
 */
public void addItems(double anyTax){
    double salesTax = anyTax;
    newList.setArray(salesTax);
    System.out.println("Sales Receipt");
    System.out.println("--------------");
    newList.returnCostArray();
    System.out.println("Total tax: $" + newList.returnTotalTax());
    System.out.println("Total cost pre-tax: $" + newList.returnTotal());
    System.out.println("Total cost including tax: $" +  (newList.returnTotal()+newList.returnTotalTax()));
}
//public String returnArray(){
    //newList.returnArray();
//}
}

编辑:局部变量问题。我试图在第一个类中使用“return array(int AnyElement)”方法，但是当我尝试编译时，它告诉我:Input 中的 returnArray(int) 不能应用于 ()。有什么帮助吗？谢谢!谢谢!

Answer 1

totalTax = totalTax;
total = total;

尝试...

this.totalTax = totalTax;
this.total = total;

该方法内的局部变量对类顶部声明的实例变量具有支配地位，因此分配 totalTax = totalTax不执行任何操作 - 它将方法中的局部变量分配给自身。使用this.totalTax表示您想使用实例变量。

您可以在该方法中使用不同的变量名称来完全避免此类事情。

(如果您不打算在该方法中创建新变量，请参阅 MByD 的答案。)