Java编程思想组合语法

Question

package TestPackage;

class WaterSource {

private String s;

WaterSource() {

System.out.println("WaterSource()");

s = "Constructed";

}

public String toString() {

return s;

}

public class SprinklerSystem {

private String value1,value2,value3,value4;

private WaterSource source = new WaterSource();

private int i ;

private float f;

public String toString() {

return

"value1 = " + value1 + " " + "value2 = " + value2 + " " + "value3 = " + value3 + " " +

"value4 = " + value4 + "\n" + "i = " + i + " " + "f = " + f + " " +

"Source = " + source;

}

}

public static void main(String[] args) {

SprinklerSystem sprinklers = new SprinklerSystem();

System.out.println(sprinklers);

}

}

main方法第一句SprinklerSystem sprinklers = new SprinklerSystem(); eclipse报出的错是No enclosing instance of type WaterSource is accessible. Must qualify the allocation with an enclosing instance of type WaterSource (e.g. x.new A() where x is an instance of WaterSource).

请问这是为什么？

Answer 1

public class SprinklerSystem { --> public static class SprinklerSystem {   这是内部类的语法，内部静态类不需要有指向外部类的引用。但非静态内部类需要持有对外部类的引用。