Java math.random，只生成一个0？
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math.random, only generating a 0?
提问by Christopher Baldwin
The following code is only producing a 0 ;-;
以下代码仅产生 0 ;-;
What am I doing wrong?
我究竟做错了什么？
public class RockPaperSci {
public static void main(String[] args) {
//Rock 1
//Paper 2
//Scissors 3
int croll =1+(int)Math.random()*3-1;
System.out.println(croll);
}
}
Edit, Another Poster suggested something that fixed it. int croll = 1 + (int) (Math.random() * 4 - 1);
编辑，另一张海报建议了一些修复它的东西。int croll = 1 + (int) (Math.random() * 4 - 1);
Thanks, everyone!
谢谢大家！
采纳答案by Sotirios Delimanolis
You are using Math.random()which states
您正在使用Math.random()哪些州
Returns a
doublevalue with a positive sign, greater than or equal to0.0and less than1.0.
返回一个
double带正号的值，大于或等于0.0并小于1.0。
You are casting the result to an int, which returns the integer part of the value, thus 0.
您将结果强制转换为int，它返回值的整数部分，因此0。
Then 1 + 0 - 1 = 0.
然后1 + 0 - 1 = 0。
Consider using java.util.Random
考虑使用 java.util.Random
Random rand = new Random();
System.out.println(rand.nextInt(3) + 1);
回答by Rohit Jain
Math.random()generates double values between range - [0.0, 1.0). And then you have typecasted the result to an int:
Math.random()在范围 - 之间生成双精度值[0.0, 1.0)。然后您将结果类型转换为int：
(int)Math.random() // this will always be `0`
And then multiply by 3is 0. So, your expression is really:
然后乘以3is 0。所以，你的表达真的是：
1 + 0 - 1
I guess you want to put parenthesis like this:
我猜你想像这样放置括号：
1 + (int)(Math.random() * 3)
Having said that, you should really use Random#nextInt(int)method if you want to generate integer values in some range. It is more efficient than using Math#random().
话虽如此，Random#nextInt(int)如果你想在某个范围内生成整数值，你真的应该使用方法。它比使用更有效Math#random()。
You can use it like this:
你可以这样使用它：
Random rand = new Random();
int croll = 1 + rand.nextInt(3);
See also:
也可以看看：
回答by Prabhakaran Ramaswamy
public static double random()
Returns a double value with a positive sign, greater than or equal to 0.0 and less than 1.0. Returned values are chosen pseudorandomly with (approximately) uniform distribution from that range.
返回带正号的双精度值，大于或等于 0.0 且小于 1.0。返回值是伪随机选择的，具有该范围内的（近似）均匀分布。
int croll =1+(int)Math.random()*3-1;
eg
例如
int croll =1+0*-1;
System.out.println(croll); // will print always 0
回答by Suresh Atta
All our mates explained you reasons of unexpected output you got.
我们所有的伙伴都向您解释了意外输出的原因。
Assuming you want generate a random croll
假设你想生成一个随机 croll
Consider Randomfor resolution
考虑Random解决
Random rand= new Random();
double croll = 1 + rand.nextInt() * 3 - 1;
System.out.println(croll);
