Question

我是java的初学者，我试图解决下面的程序，但是得到错误，谁能告诉我我在哪里做错了？

public class TestGlass 
    { 
       public static void main(String [] args) 
       { 
          Glass milk = new Glass(15); // 15 ounces of milk 
          Glass juice = new Glass(3); // 3 ources of juice



      milk.drink(2); 
      milk.drink(1); 

      milk.report(); 

      juice.fill(6);  // went from 3 to 9 ounces 
      juice.drink(1); // now down to 8 ounces 

      juice.report();  

      juice.spill(); 

      juice.report(); 
   } 
} 

class Glass 
{ 

     int ounce;

     public void spill()
     {
       ounce = 0;
     }


     public void drink(int x){
        ounce = ounce-x;
     }

     public void fill(int x){
        ounce = ounce+x;
     }

     public int getOunce()
     {
       return ounce;  
     }


     public void report()
     {
       int x = getOunce();
       System.out.println("Glass has " + x + " ounces");
     }

}

这是错误，

TestGlass.java:5: error: constructor Glass in class Glass cannot be applied to given types;
      Glass milk = new Glass(15); // 15 ounces of milk 
                   ^
  required: no arguments
  found: int
  reason: actual and formal argument lists differ in length
TestGlass.java:6: error: constructor Glass in class Glass cannot be applied to given types;
      Glass juice = new Glass(3); // 3 ources of juice 
                    ^
  required: no arguments
  found: int
  reason: actual and formal argument lists differ in length
2 errors

Answer 1

您需要向Glass添加一个接受ounce参数的构造函数。

class Glass {
....
    public Glass (int ounce) {
        this.ounce = ounce;
    }
....
}

构造函数是使用new运算符时调用的方法。它的工作是初始化 - 创建 - 类的对象实例。具有一个或多个参数的构造函数（如此构造函数）被设置为接收值以初始化类的实例变量。

注意错误消息是如何提到构造函数的。这是因为如果你没有指定自己的构造函数，Java会添加一个不接受任何参数的默认构造函数。当你调用new时，默认的no-arg构造函数就被调用了。由于您将参数传递给no-arg构造函数，因此您收到了错误。一旦添加了自己的构造函数，默认的无参数构造函数就会消失。如果你想要一个no-arg版本（例如将ounce设置为0或者设置为默认值），你可以通过指定它和我给你的那个来恢复它 - 你可以重载构造函数（参见下面的链接）。

 class Glass {
    ....
        public Glass () {
            this.ounce = 1;  
            /* In this setup, a glass always has at least 1 ounce */
            /* If you want it be 0, you could say this.ounce = 0, or */
            /* just leave everything inside {} blank, since ounce will */
            /* default to 0 anyway */
        }

        public Glass (int ounce) {
            this.ounce = ounce;
        }
    ....
    }

调用new Glass()会调用第一个no-arg构造函数。调用new Glass(15)将调用第二个构造函数，即带参数的构造函数。

Here's a nice tutorial关于构造函数。

关于重载构造函数的

Here's a nice tutorial。

Answer 2

你需要为Glass创建一个带参数的构造函数。

class Glass { 
     int ounce;

     public Glass(int ounce) {
         this.ounce = ounce;
     }

     public void spill()
     {
       ounce = 0;
     }


     public void drink(int x){
        ounce = ounce-x;
     }

     public void fill(int x){
        ounce = ounce+x;
     }

     public int getOunce()
     {
       return ounce;  
     }


     public void report()
     {
       int x = getOunce();
       System.out.println("Glass has " + x + " ounces");
     }

}

Java程序给出了错误

2 个答案: