为什么我会为我的输出获取空值？

Question

所以我试着在网上进行研究，我有一种感觉，就是我的toString（），但它的方式让我无法想象其他任何方式。

我希望能够输出：Lexie-高度：2.6英尺。出生日期：11/5/2009

我的代码如下所示：

import java.util.*; 
class Kid { 
    String name; 
    double height; 
    GregorianCalendar bDay; 
    public Kid() { 
     this.name = "HEAD"; 
     this.height = 1; 
     this.bDay = new GregorianCalendar(1111,1,1); 
    } 

    public Kid (String n, double h, String date) { 
     StringTokenizer st = new StringTokenizer(date, "/", true); 
     n = this.name; 
     h = this.height; 
    } 
    /** 
    public String toString() { 
     return (this.name + ", Height: " + this.height + "ft., Born: " 
     + this.month + "/" + this.day + "/" + this.year); 
    } 
    */ 
    public String toString() { 
     Calendar currentDate = Calendar.getInstance(); 
     return (this.name + ", Height: " + this.height + "ft., Born: " 
     + this.bDay); 
    } 
} //end class 

调用小子类低于

class Driver { 
    public static void main (String[] args) { 
     Kid kid1 = new Kid("Lexie", 2.6, "11/5/2009"); 
     System.out.println(kid1.toString()); 
    } //end main method 
} //end class 

Answer 1

你在你的构造函数表达式是南辕北辙 - 你有n = this.name你应该有this.name = n。同样适用于this.height。此外，您目前没有设置bDay字段。因此，所有的领域确实是null。

Answer 2

尝试修改你的构造和BDAY类型：

private static final String DATE_FORMAT = "dd/MM/yyyy"; 
String name; 
double height; 
Date bDay; 

public Kid() { 
    this.name = "HEAD"; 
    this.height = 1; 
    this.bDay = new Date(); 
} 

public Kid (String n, double h, String date) { 
    DateFormat df = new SimpleDateFormat(DATE_FORMAT); 
    this.bDay = df.parse(date); 
    this.name = n; 
    this.height = h; 
} 

public String toString() { 
    DateFormat df = new SimpleDateFormat(DATE_FORMAT); 
    return (this.name + ", Height: " + this.height + "ft., Born: " 
    + df.format(this.bDay)); 
} 

Answer 3

试试这个：

public Kid (String n, double h, String date) { 
     StringTokenizer st = new StringTokenizer(date, "/"); 
     this.name = n; 
     this.height = h; 
     this.bDay = new GregorianCalendar(Integer.parseInt(st.nextToken()), Integer.parseInt(st.nextToken()), Integer.parseInt(st.nextToken())); 
    }