Java &引用;非静态变量不能从静态上下文引用此变量;创建对象时
我编写了下面的代码来测试Java中类和对象的概念Java &引用;非静态变量不能从静态上下文引用此变量;创建对象时,java,oop,inner-classes,Java,Oop,Inner Classes,我编写了下面的代码来测试Java中类和对象的概念 public class ShowBike { private class Bicycle { public int gear = 0; public Bicycle(int v) { gear = v; } } public static void main() { Bicycle bike = new Bicycle(5);
public class ShowBike {
private class Bicycle {
public int gear = 0;
public Bicycle(int v) {
gear = v;
}
}
public static void main() {
Bicycle bike = new Bicycle(5);
System.out.println(bike.gear);
}
}
为什么在编译过程中会出现以下错误
ShowBike.java:12: non-static variable this cannot be referenced from a static context
Bicycle bike = new Bicycle(5);
^
制作
ShowBike.Bicycle
static
public class ShowBike {
private static class Bicycle {
public int gear = 0;
public Bicycle(int v) {
gear = v;
}
}
public static void main() {
Bicycle bike = new Bicycle(5);
System.out.println(bike.gear);
}
}
在Java中有:“静态嵌套类”和。没有static
关键字,它是一个内部类,您需要ShowBike
的实例才能访问ShowBike.Bicycle
:
ShowBike showBike = new ShowBike();
Bicycle bike = showBike.new Bicycle(5);
静态嵌套类和普通(非嵌套)类在功能上几乎相同,只是分组方式不同而已。但是,当使用静态嵌套类时,不能将它们的定义放在单独的文件中,这将导致单个文件包含大量的类定义。Make
ShowBike.Bicycle
static
public class ShowBike {
private static class Bicycle {
public int gear = 0;
public Bicycle(int v) {
gear = v;
}
}
public static void main() {
Bicycle bike = new Bicycle(5);
System.out.println(bike.gear);
}
}
在Java中有:“静态嵌套类”和。没有static
关键字,它是一个内部类,您需要ShowBike
的实例才能访问ShowBike.Bicycle
:
ShowBike showBike = new ShowBike();
Bicycle bike = showBike.new Bicycle(5);
静态嵌套类和普通(非嵌套)类在功能上几乎相同,只是分组方式不同而已。但是,当使用静态嵌套类时,不能将它们的定义放在单独的文件中,这将导致单个文件包含大量的类定义。main方法无法访问其类的非静态成员 顺便说一下,类应该以名词命名,而不是动词。因此,更好的方法是:
private class Bicycle {
public int gear = 0;
public Bicycle(int v) {
gear = v;
}
public void showGear() {
System.out.println(gear);
}
public static void main(String[] args) {
Bicycle bike = new Bicycle(6);
bike.showGear(); // Notice that the method is named after a verb
}
}
main方法无法访问其类的非静态成员 顺便说一下,类应该以名词命名,而不是动词。因此,更好的方法是:
private class Bicycle {
public int gear = 0;
public Bicycle(int v) {
gear = v;
}
public void showGear() {
System.out.println(gear);
}
public static void main(String[] args) {
Bicycle bike = new Bicycle(6);
bike.showGear(); // Notice that the method is named after a verb
}
}
Bicycle是一个内部类,因此您需要外部类实例来创建内部类实例,如:
ShowBike sBike = new ShowBike();
Bicycle bike = sBike.new Bicycle(5);
或者,您可以简单地将
Bicycle
类声明为static
,以使当前方式正常工作。Bicycle是一个内部类,因此您需要外部类实例来创建内部类实例,如:
ShowBike sBike = new ShowBike();
Bicycle bike = sBike.new Bicycle(5);
或者,您可以简单地将
Bicycle
类声明为static
,以使当前方式正常工作。您的Bicycle类不是静态的,因此不能在非静态方法中使用。如果要在main方法中使用它,请将其更改为
private static class Bicycle
您的自行车类不是静态的,因此不能在非静态方法中使用。如果要在main方法中使用它,请将其更改为
private static class Bicycle
您需要创建内部类的外部类对象instate。或者您需要将内部类设置为静态。因此,对于内部类,不需要对象。您需要创建内部类的外部类对象instate。或者您需要将内部类设置为静态。因此,对于内部类,不需要对象