如何在 Java 类方法中访问私有变量
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How to access private variables in a Java class method
提问by ANemati
I am trying to access a private variable (x) in my method distanceFromPointbut it seems it doesn't work. How can I access it? My method is returning 0.0all the time regardless of other values.
我试图x在我的方法中访问一个私有变量 ( )distanceFromPoint但它似乎不起作用。我怎样才能访问它？0.0无论其他值如何，我的方法一直在返回。
Code
代码
public class Pointdeclare {
private static int x;
private static int y;
Pointdeclare (int x_ , int y_ ){
this.x = x_;
this.y = y_;
}
int getX(){
return x;
}
int getY(){
return y;
}
static double distanceFromZero (){
return Math.sqrt(Math.pow(x, 2) + Math.pow(y, 2));
}
double distanceFromPoint(Pointdeclare point){
int distX = point.getX()- this.x;
int distY = point.getY()- this.y;
return (double) Math.sqrt(Math.pow(distX, 2) + Math.pow(distY, 2));
}
}
Main Class
主班
public class main {
static Pointdeclare p1 = new Pointdeclare(6, 7);
static Pointdeclare p2 = new Pointdeclare(3, 7);
public static void main (String[] args){
System.out.println(p2.distanceFromZero());
System.out.print(p1.distanceFromPoint(p2));
}
}
回答by duffymo
This will work better for you:
这对你来说会更好：
package cruft;
/**
* Point2 description here
* @author Michael
* @link http://stackoverflow.com/questions/14087002/how-to-access-private-variables-in-a-java-class-method
* @since 12/29/12 6:52 PM
*/
public class Point2 {
private int x;
private int y;
Point2(int x_, int y_) {
this.x = x_;
this.y = y_;
}
int getX() {
return x;
}
int getY() {
return y;
}
double distanceFromZero() {
return distanceFromPoint(new Point2(0, 0));
}
double distanceFromPoint(Point2 point) {
int distX = point.getX()-this.x;
int distY = point.getY()-this.y;
return (double) Math.sqrt(Math.pow(distX, 2)+Math.pow(distY, 2));
}
public static void main(String[] args) {
Point2 p1 = new Point2(6, 7);
Point2 p2 = new Point2(3, 7);
System.out.println(p2.distanceFromZero());
System.out.print(p1.distanceFromPoint(p2));
}
}
回答by Kevin Bigler
I hope you find this relevant, it doesn't answer your question directly but I was recently informed my understanding of staticwas incorrect so having just researched the topic I thought maybe I could help. Staticvariables belong to a class and not its objects, objects of a class may access a static variable but no matter how many objects of the class there are there will only be one copy of the static variable. So I think what the people before me were saying is instead of p1 and p2 having their own copies of x and y both objects share the same x and y field therefore your value returned is 0. In other worlds your trying to find the distance between one location, it will always be zero. Hopefully that helps :-). I'm sorry I missed the first line of the main method. p2 should return a value as long as it isn't zero but p1 will not.
我希望你觉得这很相关，它没有直接回答你的问题，但我最近被告知我的理解static是不正确的，所以刚刚研究了这个话题，我想也许我可以提供帮助。Static变量属于一个类而不是它的对象，一个类的对象可以访问一个静态变量，但无论该类有多少个对象，都只会有一个静态变量的副本。所以我认为我之前的人所说的是，而不是 p1 和 p2 拥有自己的 x 和 y 副本，这两个对象共享相同的 x 和 y 字段，因此您返回的值是 0。在其他世界中，您试图找到之间的距离一个位置，它将永远为零。希望这有帮助:-)。很抱歉我错过了 main 方法的第一行。只要它不为零，p2 就应该返回一个值，但 p1 不会。
回答by Pointy
You declared "x" and "y" static, which means that they're class variables, not instance variables.
您声明了 "x" 和 "y" static，这意味着它们是类变量，而不是实例变量。
Because of that, every new call to the constructor will overwrite the old values. Thus distanceFromPointalways returns zero because there's only one xand one y.
因此，每次对构造函数的新调用都会覆盖旧值。因此distanceFromPoint总是返回零，因为只有一x和一y。
回答by moonwave99
You shouldn't declare your class fields as static, just leave them private.
您不应该将您的类字段声明为static，只需将它们保留即可private。
Btw consider using Pointor Point2Dnative classes from java.awt.geompackage.
顺便说一句，考虑使用包中的Point或Point2D本机类java.awt.geom。
回答by TieDad
The problem is not due to private, instead, it's because of static. x is static. In your method, you should use x as:
问题不是由于私有，而是由于静态。x 是静态的。在您的方法中，您应该将 x 用作：
int distX = point.getX()- Pointdeclare.x; // You could use this.x because x is static.
