參數將不會傳遞到目標

Question

public class BottledWaterTester { 
public static void main (String args[]) 
{ 
    BottledWaterCalculator tester = new BottledWaterCalculator("USA", 350000000, 190.0, 8.5, 12.0); 


    System.out.println("The country is " + tester.getCountryName()); 
    System.out.println("The population is " + tester.getPopulation()); 
    System.out.println("The number of times the bottles circle the Equator is " + tester.getNumberCircled()); 
    System.out.println("The average length of a bottle is " + tester.getLength()); 
    System.out.println("The average volume of a bottle is " + tester.getVolume()); 
} 

}

所以我上面這段代碼。但是，當我運行它，我得到這個輸出：

*運行：

該國爲空

人口爲0

瓶繞赤道的次數爲0.0

瓶子的平均長度爲0.0

瓶子的平均容積爲0.0

BUILD SUCCESSFUL（總時間：0秒）*

原因？我明確地將值傳遞給我的測試器對象。這裏的構造函數定義如下：

public class BottledWaterCalculator { 

//instance vars 
private String countryName; 
private int population; 
private double numberCircled; 
private double avgLength; 
private double avgVolume; 

//constructor 
// note: constructor name must always be same as public class name, or else it's a method 
public BottledWaterCalculator(String country, int pop, double number, double lengthAvg, double volumeAvg) 
{ 
    country = countryName; 
    pop = population; 
    number = numberCircled; 
    lengthAvg = avgLength; 
    volumeAvg = avgVolume; 
} 

我真的很新來編程，所以我不明白髮生了什麼事情。變量

Answer 1

public BottledWaterCalculator(String country, int pop, double number, double lengthAvg, double volumeAvg) 
{ 
    countryName = country ; 
    population= pop; 
    numberCircled = number ; 
    avgLength = lengthAvg; 
    avgVolume = volumeAvg ; 
} 

錯誤的順序，你是構造函數的參數分配值，而不是對象一個

Answer 2

在你的構造翻轉變量賦值。例如：

countryName = country; 

您當前正在設置要傳入的局部變量值。 （裏面全是空/空/未分配）

Answer 3

變化下面的代碼：

public class BottledWaterCalculator { 

//instance vars 
private String countryName; 
private int population; 
private double numberCircled; 
private double avgLength; 
private double avgVolume; 

//constructor 
// note: constructor name must always be same as public class name, or else it's a method 
public BottledWaterCalculator(String country, int pop, double number, double lengthAvg, double volumeAvg) 
{ 
    countryName = country; 
    population = pop; 
    numberCircled = number ; 
    avgLength = lengthAvg ; 
    avgVolume = volumeAvg ; 
} 

Answer 4

你需要指定這個關鍵字，而分配給構造函數。