调用后未擦除方法中的Java变量
我真的需要解释我创建的代码的行为。
这里的变量preyPred:private static double[] preyPredLV(double[] preyPred, double[] a, double[] b, int n)
是否是方法preyPredLV的本地变量
因为,当我在调用该方法的过程中对其进行操作,然后针对不同的n再次调用该方法时,它不会将preyPredDefault赋值为preyPred的值,但它使用以前调用中自己的值。当方法返回输出值时,它以前的值不应该被丢弃,而不应该是在下一次调用中分配的新值吗?有人能解释一下吗?谢谢!
全部代码:
public class Main {
public static void main(String[] args) {
double[] preyPredDefault = {300, 20};
double[] a = {0.1, 0.01};
double[] b = {0.01, 0.00002};
int n = 1;
double[] result = preyPredLV(preyPredDefault, a, b, n);
System.out.println("After "+n+" generations: Hares = "+result[0]+" and Lynx = "+result[1]);
n = 2;
result = preyPredLV(preyPredDefault, a, b, n);
System.out.println("After "+n+" generations: Hares = "+result[0]+" and Lynx = "+result[1]);
}
private static double[] preyPredLV(double[] preyPred, double[] a, double[] b, int n) {
double[] preyPredOld = new double[2];
System.out.println("n = "+n);
System.out.println("preyPred[0] = "+preyPred[0]);
System.out.println("preyPred[1] = "+preyPred[1]);
for(int iteration = 0; iteration < n; iteration++){
preyPredOld[0] = preyPred[0];
preyPredOld[1] = preyPred[1];
preyPred[0] = preyPredOld[0] * (1 + a[0] - a[1]*preyPredOld[1]);
preyPred[1] = preyPredOld[1] * (1 - b[0] + b[1]*preyPredOld[0]);
}
return preyPred;
}
}
结果:
n = 1
preyPred[0] = 300.0
preyPred[1] = 20.0
After 1 generations: Hares = 270.00000000000006 and Lynx = 19.92
n = 2
preyPred[0] = 270.00000000000006
preyPred[1] = 19.92
After 2 generations: Hares = 219.31183648512007 and Lynx = 19.726535847029762
# 1 楼答案
Java中的数组不会作为副本传递。它们作为对数组的引用传递,然后在调用方和方法之间共享
因此,如果从方法内部更新数组,这是一个就地更新,任何其他对该数组有引用的人都可以看到这些更改
如果您想避免这种情况,请创建一个“防御副本”(使用Arrays.copyOf),并仅对其进行更改