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[英]How can I pass an argument to one implementor of an Interface but not the others (without passing it in the constructor)?
[英]How can I pass argument in the constructor?
我正在做一個簡單的Java作業。 看來我的語法和邏輯正確。 但是,構造函數無法理解我嘗試傳遞的參數,這就是所有計算錯誤的原因。 我已經附上了輸出。 有人知道如何解決此問題嗎? 任何幫助將不勝感激。 謝謝!
public class DT_CarStats
{
private double gallons;
private double mpg;
private double ppg;
public DT_CarStats(double gallons, double mpg, double ppg)
{
gallons = gallons;
mpg = mpg;
ppg = ppg;
}
public double CostPer100()
{
return 100 / (mpg * ppg);
}
public double MaxDistance()
{
return mpg * gallons;
}
}
import java.util.Scanner;
public class DT_CarStatsTester
{
public static void main(String[] args)
{
Scanner scannerObject = new Scanner(System.in);
double gallons, mpg, ppg;
System.out.printf("******************************************* \n");
System.out.printf("* Welcome to my Distance to Empty App * \n");
System.out.printf("******************************************* \n");
System.out.printf("Please enter the number of gallons of gas in the tank: ");
gallons = scannerObject.nextDouble();
System.out.printf("Please enter the fuel efficiency (miles per gallon): ");
mpg = scannerObject.nextDouble();
System.out.printf("Please enter the price of gas per gallon: ");
ppg = scannerObject.nextDouble();
DT_CarStats cs = new DT_CarStats(gallons,mpg,ppg);
System.out.printf("\n");
System.out.printf("To drive 100 miles, it will cost $" + cs.CostPer100() + ". \n");
System.out.printf("The car can currently drive a maximum of " + cs.MaxDistance() + " miles. \n");
System.out.printf("******************************************* \n");
System.out.printf("* Thanks for using our App, Safe Travels! * \n");
System.out.printf("******************************************* \n");
}
}
樣品運行:
*******************************************
*******************************************
* Welcome to my Distance to Empty App *
*******************************************
Please enter the number of gallons of gas in the tank: 17.6
Please enter the fuel efficiency (miles per gallon): 24.8
Please enter the price of gas per gallon: 2.36
To drive 100 miles, it will cost $Infinity. ==> This is wrong, should be $9.52
The car can currently drive a maximum of 0.0 miles. ==> This should be 436.48 miles
*******************************************
* Thanks for using our App, Safe Travels! *
*******************************************
使用this
來指定您的意思是類字段,而不是構造函數參數,因為它們的名稱相同。
public DT_CarStats(double gallons, double mpg, double ppg)
{
this.gallons = gallons;
this.mpg = mpg;
this.ppg = ppg;
}
gallons = gallons;
mpg = mpg;
ppg = ppg;
提示:在這段代碼中, gallons
, mpg
和ppg
什么?
它們是參數! 無論它們位於=
哪一側,它們始終是參數。 =
左側的變量名沒有特殊處理。
要訪問這些字段,請使用this
:
this.gallons = gallons;
this.mpg = mpg;
this.ppg = ppg;
或在字段中為參數指定不同的名稱。
此處,實例變量被方法參數覆蓋。 因此,要使用方法參數區分實例變量(兩個名稱相同時),請在構造函數中使用“ this”關鍵字。
this.gallons = gallons;
在您的情況下,方法參數再次分配給一個值,而實例變量保持不變,因此值是錯誤的
在構造函數中,您要引用與傳入參數同名的字段。 您應該使用“ this”關鍵字來確保設置對象的變量this.gallons =加侖等。
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