必须使用 GeoLocation 类型的封闭实例来限定分配

Question

我收到此错误 -

无法访问 GeoLocation 类型的封闭实例。必须使用 GeoLocation 类型的封闭实例来限定分配（例如 x.new A()，其中 x 是 GeoLocation 的一个实例）。此错误即将出现 new ThreadTask(i) 。我不知道为什么会这样。任何建议将不胜感激。

public class GeoLocation {
    public static void main(String[] args) throws InterruptedException {
        int size = 10;

        // create thread pool with given size
        ExecutorService service = Executors.newFixedThreadPool(size); 

        // queue some tasks
        for(int i = 0; i < 3 * size; i++) {
            service.submit(new ThreadTask(i));
        }

        // wait for termination        
        service.shutdown();
        service.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS); 
    }

    class ThreadTask implements Runnable {
        private int id;

        public ThreadTask(int id) {
            this.id = id;
        }

        public void run() {
            System.out.println("I am task " + id);
        }
    }

}

Answer 1

发生此错误是因为您尝试创建内部类 service.submit(new ThreadTask(i)); 的实例 没有创建主类的实例..

要解决这个问题，请先创建主类的实例：

GeoLocation outer = new GeoLocation();

然后创建您要调用的类的实例，如下所示：

service.submit(outer.new ThreadTask(i));

Answer 2

另一种选择，也是我更喜欢的选择，是将内部类设置为静态。

public static class ThreadTask implements Runnable { ... }

Answer 3

创建内联类static。

public class OuterClass {

    static class InnerClass {
    }

    public InnerClass instance = new OuterClass.InnerClass();
}

那么就可以如下实例化内部类：

new OuterClass.InnerClass();

Answer 4

做这个结构：

文件GeoLocation.java

public class GeoLocation {

    public static void main(String[] args) throws InterruptedException {

        int size = 10;

        // create thread pool with given size
        ExecutorService service = Executors.newFixedThreadPool(size); 

        // queue some tasks
        for(int i = 0; i < 3 * size; i++) {
            service.submit(new ThreadTask(i));
        }

        // wait for termination        
        service.shutdown();
        service.awaitTermination(Long.MAX_VALUE, TimeUnit.DAYS); 
    }

}

文件ThreadTask.java

public class ThreadTask implements Runnable {
    private int id;

    public ThreadTask(int id) {
        this.id = id;
    }

    public void run() {
        System.out.println("I am task " + id);
    }
}

Answer 5

您需要创建父类的实例才能创建内部类的实例。这是一个例子：

package RandomTests;

public class FinalConstructorTest {


    public static void main (String [] arg){
        FinalConstructorTest fct= new FinalConstructorTest();
        InnerClass1 f1= fct.new InnerClass1(99);
        InnerClass2 f2= fct.new InnerClass2();
    }

    class InnerClass1{
        private final int num2;

        protected InnerClass1(int num){
            num2= num;
            System.out.println("num2= "+ num2);
        }
    }
    class InnerClass2{
        //private static final int x; //Doesn't work
        private final int y; 

        {
            y= 5;
            System.out.println("y= "+ y);
        }
    }
}

Answer 6

如果您从静态方法或类似方法访问非静态成员，也可能会发生这种情况。 以下是两个不同的方面，一个是导致错误的，另一个是已解决的代码。 只需将其他设置为“静态”类即可

package Stack;

import java.util.Stack;
import java.util.*;

public class StackArrList {

    public static void main(String[] args) {


        Scanner in = new Scanner(System.in);

        Stack S = new Stack();
        System.out.println("Enter some integers and keep 0 at last:\n");
        int n = in.nextInt();

        while (n != 0) {
            S.push(n);
            n = in.nextInt();
        }
        System.out.println("Numbers in reverse order:\n");

        while (!S.empty()) {

            System.out.printf("%d", S.pop());
            System.out.println("\n");

        }

    }

    public class Stack {
        final static int MaxStack = 100;
        final static int Value = -999999;
        int top = -1;
        int[] ST = new int[MaxStack];

        public boolean empty() {
            return top == -1;
        }

        public int pop() {

            if (this.empty()) {
                return Value;
            }
            int hold = ST[top];
            top--;
            return hold;
        }

        public void push(int n) {
            if (top == MaxStack - 1) {
                System.out.println("\n Stack Overflow\n");
                System.exit(1);
            }
            top++;
            ST[top] = n;

        }

    }

}

这会引发错误StackArrList 类型的封闭实例不可访问。必须使用 StackArrList 类型的封闭实例来限定分配（例如 x.new A()，其中 x 是 StackArrList 的实例）。并且不允许创建 Stack 类的实例

当您将 class Stack 设置为 static class Stack 时会正常工作，不会出现任何错误。

package Stack;

import java.util.Stack;
import java.util.*;

public class StackArrList {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);

        Stack S = new Stack();
        System.out.println("Enter some integers and keep 0 at last:\n");
        int n = in.nextInt();

        while (n != 0) {
            S.push(n);
            n = in.nextInt();
        }
        System.out.println("Numbers in reverse order:\n");

        while (!S.empty()) {

            System.out.printf("%d", S.pop());
            System.out.println("\n");

        }

    }

    static class Stack {
        final static int MaxStack = 100;
        final static int Value = -999999;
        int top = -1;
        int[] ST = new int[MaxStack];

        public boolean empty() {
            return top == -1;
        }

        public int pop() {

            if (this.empty()) {
                return Value;
            }
            int hold = ST[top];
            top--;
            return hold;
        }

        public void push(int n) {
            if (top == MaxStack - 1) {
                System.out.println("\n Stack Overflow\n");
                System.exit(1);
            }
            top++;
            ST[top] = n;

        }

    }

}