Java出现No enclosing instance of type E is accessible. Must qualify the allocation with an enclosing

最近在看Java，在编译写书上一个例子时，由于书上的代码只有一部分，于是就自己补了一个内部类。结果编译时出现：No enclosing instance of type E is accessible. Must qualify the allocation with an enclosing instance of type E(e.g.  x.new A() where x is an instance of E). E指代我写的那个内部类。

根据提示，没有可访问的内部类E的实例，必须分配一个合适的内部类E的实例（如x.new A()，x必须是E的实例。）看着这句提示，我就纳闷了，我已经用new实例化了这个类，为什么还不行呢。

于是百度谷歌了一下相关资料。原来我写的内部类是动态的，也就是开头以public class开头。而主程序是public static class main。在Java中，类中的静态方法不能直接调用动态方法。只有将某个内部类修饰为静态类，然后才能够在静态类中调用该类的成员变量与成员方法。所以在不做其他变动的情况下，最简单的解决办法是将新写的类的public class改为public static class.

 

package jave;

public class Point {
	private double x;
	private double y;
	Point(double x1, double y1){
		x = x1;
		y = y1;
	}
	public double getX() {
		return x;
	}
	public double getY() {
		return y;
	}
	public void setX(double i) {
		x = i;
	}
	public void setY(double i) {
		y = i;
	}
	
	
public static class Circle{
		private Point o;//圆心
		private double radius;//半径
		//构造函数
		Circle(Point p, double r) {
			o = p;
			radius = r;
		}
		//构造函数的重载
		Circle(double r) {
			o = new Point(0.0, 0.0);//初始化圆心在原点
			radius = r;
		}
		//判断该点在不在圆里
		boolean contains(Point p) {
			double x = p.getX() - o.getX();
			double y = p.getY() - o.getY();
			if((x*x + y*y) > radius*radius)
				return false;
			else 
				return true;
		}
		public void setO(double x, double y) {
			o.setX(x);
			o.setY(y);
		}
		public Point getO() {
			return o;
		}
		public double getRadius() {
			return radius;
		}
		public void setRadius(double r) {
			radius = r;
		}
		public double area() {
			return 3.14 * radius *radius;
		}
	}
	
	
	
	public static void main(String[] args) {
		Circle c1 = new Circle(new Point(1.0, 2.0), 2.0);
		Circle c2 = new Circle(5.0);
		System.out.println("c1:(" + c1.getO().getX() + "," + c1.getO().getY() + ")," + c1.getRadius());
		System.out.println("c2:(" + c2.getO().getX() + "," + c2.getO().getY() + ")," + c2.getRadius());
		System.out.println("c1 area = " + c1.area());
		System.out.println("c2 area = " + c2.area());
		c1.setO(5, 6);
		c2.setRadius(9.0);
		System.out.println("c1:(" + c1.getO().getX() + "," + c1.getO().getY() + ")," + c1.getRadius());
		System.out.println("c2:(" + c2.getO().getX() + "," + c2.getO().getY() + ")," + c2.getRadius());
		System.out.println("c1 area = " + c1.area());
		System.out.println("c2 area = " + c2.area());
		
		
		Point p1 = new Point(5.2, 6.3);
		System.out.println(c1.contains(p1));
		System.out.println(c1.contains(new Point(10.9, 9.0)));

	}

}

即将public class Circle 改为public static class Circle， public void main(String[] args)改为public static void main(String[] args)。