[英]Understanding java code (abstract classes, extends function)
我試圖理解這段代碼......
這是原始代碼:
public class understanding {
public static void main(String[] args) {
int n = 5;
Shape[] s = new Shape[n];
for (int i = 0; i < n; i++) {
s[i] = getShape(i);
System.out.println(s[i]);
}
System.out.println(compute(s));
}
public static Shape getShape(int i) {
if (i % 2 == 0) {
return new Circle(i);
} else {
return new Polygon(i, i);
}
}
public static double compute(Shape[] a) {
double nc = 0;
for (int i = 0; i < a.length; i++) {
nc += a[i].getMeasure();
System.out.println(a[i].getMeasure());
}
return nc;
}
}
public abstract class Shape {
protected abstract double getMeasure();
}
public class Polygon extends Shape {
private double x;
private double y;
Polygon(double x_, double y_) {
x = x_;
y = y_;
}
public double getMeasure() {
return 2 * (x + y);
}
}
public class Circle extends Shape {
private double r;
Circle(double r_) {
r = r_;
}
public double getMeasure() {
return 2 * r;
}
}
有人可以幫我理解這段代碼如何返回28.但也解釋了我被卡住的部分......
干運行時,我卡在這里:
for(int i=0;i<n;i++){ // i=0, i<5, i++
s[i] = getShape[i] // i=0, go to getShape class
...
getShape(i) //i=0
if (i%2==0) //TRUE so..
return new Circle(i); //bc the boolean is True, go to Circle() class
...
Circle extends Shape{
private double r;
Circle(double r_){ //I get lost here.. is r=0 now (because r_=i and r=r_)?
r = r_;
}
main
循環依次產生Circle(0)
, Polygon(1,1)
, Circle(2)
, Polygon(3,3)
, Circle(4)
; 這是因為對於偶數, i % 2
為0,對於奇數則為1。 對於多邊形, measure
返回2 *(x + y),因此對於(1,1),您有2 *(1 + 1)= 4,對於(3,3),您有2 *(3 + 3)= 12對於圓圈, measure
返回2 * r,所以對於(0)你有2 * 0 = 0,對於(2)你有2 * 2 = 4,對於(4)你有2 * 4 = 8。 + 4 + 4 + 12 + 8 = 28。
對於您迷路現場, getShape(i)
傳遞的價值i
來getShape
; 當i
= 0時,這會創建一個Circle,因此將0
傳遞給Circle構造函數,然后Circle(0)
將r
設置為0.如果i
= 2則ditto,則r
= 2,依此類推。
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