Question

这是我的完整代码

package user;
public class User {
private String userID,emailAddress;
private int numOfAccesses;
public static int counter=0;
public User(String iD,String emailA,int nOA){
userID=iD;
emailA=emailAddress;
nOA=numOfAccesses;
counter++  
}
public User(String aID,String aEmail){
this(aID,aEmail,0);
}
public User(){
this(null,null,0); 
}
public String getInfos(){
String message =("user ID "+userID+"\n"+"email address is "+emailAddress+"\n"+"number of accesses "+numOfAccesses);
return message;
}   

public void  setInfos(String setID,String setEmail){
   setID=userID;
   setEmail=emailAddress;

}
public int getCounter(){
return counter;

}
 public void updateNumOfAccesses(){
   numOfAccesses++;

 }
  public class testUser extends User{
    User user1=new User();
    System.out.println("counter is "+user1.getCounter);

 } 
public static void main(String[] args) {

}

   }

我很抱歉我是java中的菜鸟，但我真的很困惑，为什么我能调用getCounter方法，而我明确做对了。是因为继承？或者我没有使用柜台吗？请帮忙

Answer 1

您有语法错误

你想要

System.out.println("counter is "+user1.getCounter ());

正在调用方法

同时更改此代码

 public class testUser extends User{
    User user1=new User();
    System.out.println("counter is "+user1.getCounter);

 } 
 public static void main(String[] args) {

 }

到

public static void main(String[] args) {
    User user1=new User();
    System.out.println("counter is "+user1.getCounter ());
}

另一个错误是

counter++  is not terminated with a `;`

Answer 2

public class User {
    ...

    class TestUser extends User {
        User user1 = new User();

        public void someMethodName() {
            System.out.println("counter is " + user1.getCounter());
        }

    }

    public static void main(String[] args) {
        User u1 = new User();
        TestUser tu1 = u1.new TestUser();
        tu1.someMethodName();
    }

}

输出：

counter is 3

正在调用User（）三次创建。

用户u1 =新用户（）; // counter = 1
TestUser tu1 = u1.new TestUser（）; // counter = 3
当JVM看到extends User时，它会调用User类的构造函数来递增计数器。
然后，User user1 = new User();再次递增计数器

为什么我在调用getCounter方法时出错？

2 个答案: