Question

我有以下设置，我认为可以使用但在我的IDE（Android Studio）中出错：

// MyClass1.java
public class MyClass1{
    public MyClass1(){}
    public class MyNestedClass1{}
}

// MyClass2.java
public class MyClass2{
    public static MyClass1 MY_CLASS1 = new MyClass1();
    public MyClass2(){
        new MY_CLASS1.MyNestedClass1(); //Error
    }
}

具体的IDE错误是：

无法解析符号MyNestedClass1

Answer 1

符号是

MY_CLASS1.new MyNestedClass1(); //No Error

语法是

<Expression that resolves to a reference of the enclosing class>.new [Name of nested inner class](..)

Answer 2

// MyClass2.java
public class MyClass2{
    public static MyClass1 MY_CLASS1 = new MyClass1();//you have already instantiated MyClass1 by new operator here
    public MyClass2(){
        MY_CLASS1.new MyNestedClass1(); //so now intantiate only inner class by new operator
    }
}

Answer 3

您可以将嵌套类定义为static。这将允许实例化独立于 MyClass1 。

// MyClass1.java
public class MyClass1{
    public MyClass1(){}
    public static class MyNestedClass1{}
}

// MyClass2.java
public class MyClass2{
    public MyClass2(){
        /* One Way. */
        new MyClass1.MyNestedClass1();
        /* Or Another. */
        new MyNestedClass1();
    }
}

实例化另一个类的内部类

3 个答案: