Question

我有这个令人惊讶且好看的课程：

public class SayingsHolder extends Application{

    ArrayList<String> SayingsList = new ArrayList<String>(){{
        SayingsList.add("1");
        SayingsList.add("2");

    }};

    public ArrayList<String> getSayingsList() {
        return SayingsList;
    }
}

现在我试图通过以下方式调用我的getSayingsList FragmentStatePagerAdapter方法{/ 1}}。

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {   
    final SayingsHolder holder = (SayingsHolder).getApplication();
}

现在一切都很好，但是当我像这样编写代码时：

 private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {   
        final SayingsHolder holder = (SayingsHolder).getApplication();
        holder.getSayingsList();
    }

它说：

Syntax error on token "getSayingsList", Identifier expected after this token

问题在于holder根本不起作用。我的意思是，当我输入holder.时，getSayingsList根本没有显示。

我在这里缺少什么？我知道这是一个非常小的问题，但似乎我无法发现它。我的活动extends FragmentActivity，如果它很重要

似乎我在这里遗漏了一些东西。我无法在我的活动中将我的方法称为任何地方。我开始赏金，因为我需要一个例子。

Answer 1

一个简单的答案是“课堂体内不允许发表声明”。对您来说，最简单的修复方法是创建一个实例列表变量，如。

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {   
    final SayingsHolder holder = (SayingsHolder).getApplication();
    ArrayList<String> sayingsList = holder.getSayingsList();
}

这只是一个选择。您也可以将此holder.getSayingsList();移动到方法体或静态块。像所有其他问题一样，程序问题是语法错误。

根据Java语法，类主体可以包含成员声明，静态块，方法声明，另一个类声明，构造函数等。您可以在http://docs.oracle.com/javase/specs/jls/se7/html/jls-18.html上阅读此内容。这可能会造成混淆，因此请先参考http://docs.oracle.com/javase/specs/jls/se7/html/jls-2.html。这给出了关于每个符号的想法。

public class ScreenSlidePagerAdapter {
    // This is a member declaration. So "holder" is now a class member.
    final SayingsHolder holder = (SayingsHolder).getApplication();

    // This is a constructor
    public ScreenSlidePagerAdapter(){
    }

    // An inner class
    class InnerScreenSlidePagerAdapter{
    }

    // A method
    public void aMethod() {
    }

    // This is a static block
    static {
    }

}

所有这些都适用于课堂内。但在您的情况下，您正在尝试向类主体添加语句。这不符合语法规则

private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {       
    final SayingsHolder holder = (SayingsHolder).getApplication(); //This line a member declaration. And a valid sysntax. So no issues here

    holder.getSayingsList(); // This is a statement. So this line creates issue as its not part of a class body. 
                // Statements should be enclosed within a method body or static block or for an assigment.

    //But instead if you say it like
    List<String> sayingsList = holder.getSayingsList(); // Now it became a filed(member) declaration. You are trying to declare a member names "sayingsList" just like you created "holder" above
    //So now we converted the statement to a member declaration
}

希望这有帮助

Answer 2

在类的定义中，您可以拥有方法和属性。 “holder.getSayingsList（）;”是一个属于方法内的语句。它不能单独定义一个类。

以下是一个例子：

public class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter {   
    final SayingsHolder holder = SayingsHolder.getApplication();

    /* You cannot use holder here. Statements like this must be inside a method.
    holder.getSayingsList();
     */

    /* For the same reason, you cannot do this here:
    System.out.println("Hello World!");
     */

    /* You CAN use holder in an instance method */
    public void foo() {
        holder.getSayingsList();
    }

    /* You can use it in a class method, but you must instantiate a ScreenSlidePagerAdapter object first */
    public static void main(String[] args) {

        ScreenSlidePagerAdapter obj = new ScreenSlidePagerAdapter();
        obj.getHolder().getSayingsList();

        /* you can do this too */
        obj.foo();

    }

    //getter for the holder variable
    public SayingsHolder getHolder() {
        return holder;
    }

}

Answer 3

您不能拥有非方法声明的语句。 “holder.getSayingsList（）;”语句必须在方法或静态初始化块中。

无法参考我的get方法

3 个答案: