Question

以下是我的代码，我已经发表评论来解释我面临的问题。

我应该导入别的东西吗？我正在使用jGrasp编译器？

import java.awt.*;
import java.applet.*;
import java.lang.*;
/*this is just a test class to learn how to use substring. I was trying to use substring 
   to play around with strings in this case my dogs name. I was doing exercises on codingbat.com
  and came across the substring method. 
*/
public class Donna extends Applet {

    String DogName = "Donna Peluda";       // declare the String variable DogName
    String FirstDog = "";                  // declare FirstDog String variable blank
    FirstDog = DogName.substring( 0, 2);   // I get "Donna.java:9: error: <identifier> expected" 
    // if I comment out line 9 it prints "Donna Peluda" ok
    // Ive tried examples from the web and get the same error and spent 2 evenings on this so 

    public void paint(Graphics d) {
        d.drawString(DogName + FirstDog ,25, 25);//print the result to the applet
    }
}

Answer 1

这不适合分配。如果你真的想在那里做，那试试这个

public class Donna extends Applet
{
    String dogName = "Donna Peluda";
    String FirstDog = "";
    {
        FirstDog = DogName.substring(0, 2);
    }

    .
    .
    .

Answer 2

类主体（第一个开括号和最后一个右括号之间的所有内容）只允许包含以下工件：

class MyClass extends MySuperClass implements YourInterface {
    // field, constructor, and
    // method declarations
}

该行

FirstDog = DogName.substring( 0, 2);

字段声明部分中不允许

。您可以将该行移动到构造函数中。或者直接初始化字段：

String FirstDog = DogName.substring( 0, 2);

另请参阅http://docs.oracle.com/javase/tutorial/java/javaOO/classdecl.html以获取详细参考。

Answer 3

试试这个：

String DogName = "Donna Peluda";
String FirstDog = getFirst();

public String getFirst()
{
    return DogName.substring( 0, 2);
}

Answer 4

因为在init Donna时，jvm无法确保这三个声明的调用顺序。

String DogName = "Donna Peluda";     
String FirstDog = "";
FirstDog = DogName.substring( 0, 2);

但是在成员分配后可以调用{}，所以：

String DogName = "Donna Peluda";
String FirstDog = "";
{             
    FirstDog = DogName.substring(0, 2);
}

为什么我会收到错误：错误：第9行预期的<identifier>我错过了导入</identifier>

4 个答案:

因为在init Donna时，jvm无法确保这三个声明的调用顺序。