使用Collections.shuffle的带有两个元素的Java随机洗牌列表 import java.util.ArrayList； 导入java.util.array； 导入java.util.Collections； 导入java.util.Random； 公共类洗牌师{ 公共静态void main（字符串[]args）{ 字符串[]文件={“1”，“2”}； 长种子=3； ArrayList fileList=新的ArrayList（Arrays.asList（file））； 对于（int i=0；i

而言，问题不在于

shuffle

——而在于带有小种子的

Random

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.Random;

public class ShuffleList {
  public static void main(String[] args) {
    String [] file = {"1","2"};
    long seed = 3;
    ArrayList<String> fileList = new ArrayList<String>(Arrays.asList(file));
    for (int i=0; i<200; i++) {
      Collections.shuffle(fileList, new Random(seed));
      seed = seed +1;
      System.out.println(seed + "," + fileList);
    }
  }
}

import java.util.Random；
公开课考试{
公共静态void main（字符串[]args）{
int-total=0；
对于（int seed=0；seed<4000；seed++）{
随机rng=新随机（种子）；
总计+=下一个月的租金（2）；
}
系统输出打印项次（总计）；
}
}

您预期的输出大约为2000—大约一半对

nextInt

的调用应该返回0，大约一半应该返回1。相反，它是4000—每个调用都返回1

使用seeds[10000，13999]你可以得到240个——因此，返回0的电话远远多于返回1的电话

使用种子[100000，103999）你得到3226-变得更好

使用种子[1000000103999]你可以得到2105个-更好

---

我对RNG的数学知识还不足以解释为什么会发生这种情况，但它看起来确实像是

java.util.Random

对于小种子来说有点不好。

对于两个元素的列表，shuffle所做的是用一个随机位置交换一个元素：

import java.util.Random;

public class Test {
    public static void main(String[] args) {
        int total = 0;
        for (int seed = 0; seed < 4000; seed++) {
            Random rng = new Random(seed);
            total += rng.nextInt(2);
        }
        System.out.println(total);
    }
}

因此，您所证明的是，对于3到203之间的种子，对

rnd.nextInt（2）

的第一次调用返回1。如果您在所有测试中使用随机种子或使用相同的随机实例，您将得到不同的结果

例如，将

new Random（seed）

更改为

new Random（3）

（实际上，创建该实例一次并将其传递给Collections.shuffle会更有意义）生成：

swap(list, 2-1, rnd.nextInt(2));

+乔恩和埃兰各1人

如果你想让你的代码正常工作，不要每次通过循环都实例化Random，在循环之前创建一个实例并传递它。Random就是这样设计的，并且在每次调用之前不会改变种子

例如

4,[1, 2]
5,[1, 2]
6,[2, 1]
7,[2, 1]
8,[1, 2]
9,[1, 2]
10,[1, 2]
11,[1, 2]
12,[2, 1]
13,[2, 1]
14,[2, 1]
15,[1, 2]
16,[1, 2]
17,[2, 1]
18,[1, 2]
19,[2, 1]
20,[2, 1]
21,[1, 2]
22,[1, 2]
23,[1, 2]
24,[2, 1]
25,[2, 1]
26,[2, 1]
27,[2, 1]
28,[2, 1]
29,[1, 2]
30,[1, 2]
31,[2, 1]
32,[2, 1]
33,[1, 2]
34,[2, 1]
35,[2, 1]
36,[2, 1]
37,[1, 2]
38,[2, 1]
39,[2, 1]
40,[1, 2]
41,[2, 1]
42,[1, 2]
43,[2, 1]
44,[1, 2]
45,[1, 2]
46,[2, 1]
47,[2, 1]
48,[1, 2]
49,[2, 1]
50,[2, 1]
51,[1, 2]
52,[1, 2]
53,[2, 1]
54,[2, 1]
55,[2, 1]
56,[2, 1]
57,[1, 2]
58,[2, 1]
59,[1, 2]
60,[1, 2]
61,[2, 1]
62,[2, 1]
63,[1, 2]
64,[2, 1]
65,[1, 2]
66,[2, 1]
67,[1, 2]
68,[2, 1]
69,[1, 2]
70,[2, 1]
71,[1, 2]
72,[1, 2]
73,[2, 1]
74,[1, 2]
75,[2, 1]
76,[1, 2]
77,[2, 1]
78,[1, 2]
79,[2, 1]
80,[1, 2]
81,[2, 1]
82,[2, 1]
83,[1, 2]
84,[1, 2]
85,[1, 2]
86,[2, 1]
87,[2, 1]
88,[1, 2]
89,[1, 2]
90,[2, 1]
91,[1, 2]
92,[1, 2]
93,[2, 1]
94,[1, 2]
95,[1, 2]
96,[1, 2]
97,[1, 2]
98,[1, 2]
99,[1, 2]
100,[1, 2]
101,[1, 2]
102,[2, 1]
103,[1, 2]
104,[2, 1]
105,[2, 1]
106,[1, 2]
107,[1, 2]
108,[1, 2]
109,[2, 1]
110,[2, 1]
111,[1, 2]
112,[2, 1]
113,[1, 2]
114,[1, 2]
115,[2, 1]
116,[2, 1]
117,[2, 1]
118,[1, 2]
119,[2, 1]
120,[1, 2]
121,[1, 2]
122,[1, 2]
123,[2, 1]
124,[1, 2]
125,[2, 1]
126,[1, 2]
127,[2, 1]
128,[2, 1]
129,[1, 2]
130,[1, 2]
131,[2, 1]
132,[2, 1]
133,[1, 2]
134,[1, 2]
135,[1, 2]
136,[2, 1]
137,[1, 2]
138,[2, 1]
139,[1, 2]
140,[2, 1]
141,[2, 1]
142,[1, 2]
143,[1, 2]
144,[2, 1]
145,[1, 2]
146,[1, 2]
147,[2, 1]
148,[2, 1]
149,[1, 2]
150,[2, 1]
151,[1, 2]
152,[1, 2]
153,[2, 1]
154,[2, 1]
155,[1, 2]
156,[2, 1]
157,[2, 1]
158,[2, 1]
159,[1, 2]
160,[1, 2]
161,[1, 2]
162,[1, 2]
163,[2, 1]
164,[2, 1]
165,[2, 1]
166,[1, 2]
167,[2, 1]
168,[2, 1]
169,[1, 2]
170,[2, 1]
171,[1, 2]
172,[2, 1]
173,[2, 1]
174,[1, 2]
175,[2, 1]
176,[1, 2]
177,[1, 2]
178,[2, 1]
179,[1, 2]
180,[2, 1]
181,[2, 1]
182,[1, 2]
183,[1, 2]
184,[2, 1]
185,[1, 2]
186,[2, 1]
187,[1, 2]
188,[2, 1]
189,[2, 1]
190,[2, 1]
191,[2, 1]
192,[2, 1]
193,[1, 2]
194,[2, 1]
195,[1, 2]
196,[2, 1]
197,[1, 2]
198,[2, 1]
199,[2, 1]
200,[2, 1]
201,[2, 1]
202,[2, 1]
203,[1, 2]

公共类ShuffleList{
公共静态void main（字符串[]args）{
字符串[]文件={“1”，“2”}；
ArrayList fileList=新的ArrayList（Arrays.asList（file））；
随机数=新随机数（3）；
对于（int i=0；i
4,[1, 2]
5,[1, 2]
6,[2, 1]
7,[2, 1]
8,[1, 2]
9,[1, 2]
10,[1, 2]
11,[1, 2]
12,[2, 1]
13,[2, 1]
14,[2, 1]
15,[1, 2]
16,[1, 2]
17,[2, 1]
18,[1, 2]
19,[2, 1]
20,[2, 1]
21,[1, 2]
22,[1, 2]
23,[1, 2]
24,[2, 1]
25,[2, 1]
26,[2, 1]
27,[2, 1]
28,[2, 1]
29,[1, 2]
30,[1, 2]
31,[2, 1]
32,[2, 1]
33,[1, 2]
34,[2, 1]
35,[2, 1]
36,[2, 1]
37,[1, 2]
38,[2, 1]
39,[2, 1]
40,[1, 2]
41,[2, 1]
42,[1, 2]
43,[2, 1]
44,[1, 2]
45,[1, 2]
46,[2, 1]
47,[2, 1]
48,[1, 2]
49,[2, 1]
50,[2, 1]
51,[1, 2]
52,[1, 2]
53,[2, 1]
54,[2, 1]
55,[2, 1]
56,[2, 1]
57,[1, 2]
58,[2, 1]
59,[1, 2]
60,[1, 2]
61,[2, 1]
62,[2, 1]
63,[1, 2]
64,[2, 1]
65,[1, 2]
66,[2, 1]
67,[1, 2]
68,[2, 1]
69,[1, 2]
70,[2, 1]
71,[1, 2]
72,[1, 2]
73,[2, 1]
74,[1, 2]
75,[2, 1]
76,[1, 2]
77,[2, 1]
78,[1, 2]
79,[2, 1]
80,[1, 2]
81,[2, 1]
82,[2, 1]
83,[1, 2]
84,[1, 2]
85,[1, 2]
86,[2, 1]
87,[2, 1]
88,[1, 2]
89,[1, 2]
90,[2, 1]
91,[1, 2]
92,[1, 2]
93,[2, 1]
94,[1, 2]
95,[1, 2]
96,[1, 2]
97,[1, 2]
98,[1, 2]
99,[1, 2]
100,[1, 2]
101,[1, 2]
102,[2, 1]
103,[1, 2]
104,[2, 1]
105,[2, 1]
106,[1, 2]
107,[1, 2]
108,[1, 2]
109,[2, 1]
110,[2, 1]
111,[1, 2]
112,[2, 1]
113,[1, 2]
114,[1, 2]
115,[2, 1]
116,[2, 1]
117,[2, 1]
118,[1, 2]
119,[2, 1]
120,[1, 2]
121,[1, 2]
122,[1, 2]
123,[2, 1]
124,[1, 2]
125,[2, 1]
126,[1, 2]
127,[2, 1]
128,[2, 1]
129,[1, 2]
130,[1, 2]
131,[2, 1]
132,[2, 1]
133,[1, 2]
134,[1, 2]
135,[1, 2]
136,[2, 1]
137,[1, 2]
138,[2, 1]
139,[1, 2]
140,[2, 1]
141,[2, 1]
142,[1, 2]
143,[1, 2]
144,[2, 1]
145,[1, 2]
146,[1, 2]
147,[2, 1]
148,[2, 1]
149,[1, 2]
150,[2, 1]
151,[1, 2]
152,[1, 2]
153,[2, 1]
154,[2, 1]
155,[1, 2]
156,[2, 1]
157,[2, 1]
158,[2, 1]
159,[1, 2]
160,[1, 2]
161,[1, 2]
162,[1, 2]
163,[2, 1]
164,[2, 1]
165,[2, 1]
166,[1, 2]
167,[2, 1]
168,[2, 1]
169,[1, 2]
170,[2, 1]
171,[1, 2]
172,[2, 1]
173,[2, 1]
174,[1, 2]
175,[2, 1]
176,[1, 2]
177,[1, 2]
178,[2, 1]
179,[1, 2]
180,[2, 1]
181,[2, 1]
182,[1, 2]
183,[1, 2]
184,[2, 1]
185,[1, 2]
186,[2, 1]
187,[1, 2]
188,[2, 1]
189,[2, 1]
190,[2, 1]
191,[2, 1]
192,[2, 1]
193,[1, 2]
194,[2, 1]
195,[1, 2]
196,[2, 1]
197,[1, 2]
198,[2, 1]
199,[2, 1]
200,[2, 1]
201,[2, 1]
202,[2, 1]
203,[1, 2]

public class ShuffleList {
  public static void main(String[] args) {
    String [] file = {"1","2"};
    ArrayList<String> fileList = new ArrayList<String>(Arrays.asList(file));

    Random random = new Random(3);
    for (int i=0; i<200; i++) {
      Collections.shuffle(fileList, random);
      System.out.println(fileList);
    }
  }
}