java java中的静态和非静态方法
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static and non static methods in java
提问by user560084
Possible Duplicate:
When should a method be static?
可能的重复：
方法什么时候应该是静态的？
i am trying to make an interface class for tube/subway ticket machine. well not for real, but for a coursework in a computer science module. i dont understand when to use static methods. i dont know much about computer sciences, but main methods seem to use static.
我正在尝试为地铁/地铁售票机制作一个接口类。不是真的，而是用于计算机科学模块中的课程作业。我不明白什么时候使用静态方法。我不太了解计算机科学，但主要方法似乎使用静态。
class UNInterfaceTest
{
public static final int NOTTING_HILL = 1;
public static final int HIGH_KEN = 2;
public static final int GLOUS = 3;
public static final int SOUTH_KEN = 4;
public static final int SLOANE = 5;
public static final int VICTORIA = 6;
public static final int ST_JAMES = 7;
public static final int WESTMINSTER = 8;
public static final int QUIT = 10;
private Input in = new Input();
private static void displayMenu()
{
System.out.println("CIRCLE LINE: Please Select the Number of Your Current Station.");
System.out.println(NOTTING_HILL + ": Nottinghill_Gate");
System.out.println(HIGH_KEN + ": High_Street_Kensignton");
System.out.println(GLOUS + ": Gloucester_Road");
System.out.println(SOUTH_KEN + ": South_Kensignton");
System.out.println(SLOANE + ": Sloane_Square");
System.out.println(VICTORIA + ": Victoria");
System.out.println(ST_JAMES + ": St_James_Park");
System.out.println(WESTMINSTER + ": Westminster");
System.out.println();
System.out.println(QUIT + ". Quit");
}
public static void run()
{
while(true)
{
displayMenu();
int option = getMenuInput();
if (option == QUIT)
{
break;
}
doOption(option);
}
}
private static void doOption(int option)
{
switch(option){
case NOTTING_HILL:
//findNottinghill_Gate();
break;
case HIGH_KEN:
//findHighStreetKensignton();
break;
case GLOUS:
//findGloucesterRoad();
break;
case SOUTH_KEN:
//findSouthKensignton();
break;
case SLOANE:
// findSloaneSquare();
break;
case VICTORIA:
//findVictoria();
break;
case ST_JAMES:
//findStJamesPark();
break;
case WESTMINSTER:
//findWestminster();
break;
default:
System.out.println("Invalid option - try again");
}
}
private int getMenuInput()
{
//KeyboardInput val = new KeyboardInput();
System.out.print("Enter menu selection: ");
int option = in.nextInt();
in.nextLine();
return option;
}
public static void main(String[] args)
{
run();
}
}
回答by AniDev
Think of a class as a cookie cutter, and an object as the cookie (an instance of the class). Static methods are methods part of the class itself (the cookie cutter), as in MyClass.myMethod();, whereas non-static methods are part of the class instances (the cookies), as in new MyClass().myMethod();.
将类视为饼干切割机，将对象视为饼干（类的实例）。静态方法是类本身（饼干切割器）的方法的一部分，如MyClass.myMethod();，而非静态方法是类实例（饼干）的一部分，如new MyClass().myMethod();。
In your case, static methods would be things specific to ticket machines in general, like calculating how much money should be deducted. Non-static methods would be things specific to a single ticket counter, such as keeping track of how many tickets it has processed.
在您的情况下，静态方法通常是特定于售票机的东西，例如计算应扣除多少钱。非静态方法将是特定于单个票务柜台的事情，例如跟踪它已处理的票数。
Here is some more information:
http://cscie160-distance.com/nonstatic.html
回答by SLaks
A staticmethod is not associated with an instance of a class.
Any method which doesn't use or modify the instance of the class it's defined on should be static.
甲static方法不与类的实例相关联。
任何不使用或修改它定义的类的实例的方法都应该是static.
回答by Matthew Flaschen
Instance methods are per-ticket machine, while static methods do something that affects all ticket machines simultaneously.
实例方法是针对每个售票机的，而静态方法会同时影响所有售票机。
Now, in your case, you may realistically only use on e at a time. But conceptually, each machine would have its own keyboard, screen, and CPU, so all the methods should be instance.
现在，在您的情况下，您实际上一次只能使用 e。但从概念上讲，每台机器都有自己的键盘、屏幕和 CPU，所以所有的方法都应该是实例。
That means you need to create a machine in main:
这意味着您需要在以下位置创建机器main：
UNInterfaceTest machine = new UNInterfaceTest();
machine.run();
Of course, you're currently writing directly to standard out (not sure what Inputreads from). A better design might be to pass in a Writerto the UNInterfaceTest constructor, then write to that (instead of System.out). That lets each machine have its own screen.
当然，您目前正在直接写入标准输出（不确定Input读取的是什么）。更好的设计可能是将 a 传递Writer给 UNInterfaceTest 构造函数，然后写入该构造函数（而不是 System.out）。这让每台机器都有自己的屏幕。
Of course, some of this information may be beyond the scope of the assignment. It should still be useful to know.
当然，其中一些信息可能超出了分配的范围。了解一下应该还是有用的。
回答by crnlx
Short answer: That is because you are not making use of your objects. You can instantiate your class as an object and run it using
简短的回答：那是因为你没有使用你的对象。您可以将您的类实例化为一个对象并使用
UNInterfaceTest unit = new UNInterfaceTest();
unit.run();
using non-static methods.
使用非静态方法。
