ArrayList索引超出范圍，但實際上不是嗎？

Question

所以我現在在我的Java代碼中遇到一個非常令人困惑的錯誤。 我只是要插入代碼的重要部分，並解釋它應該做什么：

 ArrayList<String> superstarKandidaten = new ArrayList<>(freundesliste.keySet()); //there are exactly 5 keys in freundesliste, and after checking the content of superstarKandidaten, it gives me 5 different values (everything how I wanted it to be)

現在，下面的代碼看起來有些怪異，它基本上應該讀取兩個不相同的superstarKandidaten值。

int i = 0;    
while (superstarKandidaten.size() > 1) {
                if (i + 1 > superstarKandidaten.size()) i = 0; else i++;
                System.out.println(i);
                person1 = superstarKandidaten.get(i);
                System.out.println(person1);
                if (i + 1 > superstarKandidaten.size()) i = 0; else i++;
                System.out.println(i);
                person2 = superstarKandidaten.get(i); // <-- this is where the error happens according to the error message. (this is Ausrechnen.java:24
                System.out.println(person2);
                if (person1.equals(person2)) {
                    if (i + 1 > superstarKandidaten.size()) {
                        i = 0;
                    }else i++;
                    person2 = superstarKandidaten.get(i);
                }

我不需要編寫其余代碼，因為它是不必要的，這里是輸出：

    {Knuth=null Turing Dijkstra, Hoare=null Turing Dijkstra Codd, Turing=Hoare Dijkstra, Codd=null Turing Dijkstra Knuth, Dijkstra=null} // this is freundesliste
[Knuth, Hoare, Turing, Codd, Dijkstra] //this is superstarKandidaten
1 //this is i
Hoare //this is person1
2 //this is i
Turing //this is person2
3
Dijkstra
4
Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 4 out of bounds for length 4
    at java.base/jdk.internal.util.Preconditions.outOfBounds(Preconditions.java:64)
    at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Preconditions.java:70)
    at java.base/jdk.internal.util.Preconditions.checkIndex(Preconditions.java:248)
    at java.base/java.util.Objects.checkIndex(Objects.java:372)
    at java.base/java.util.ArrayList.get(ArrayList.java:458)
    at Ausrechnen.superstar(Ausrechnen.java:24)
    at Main.main(Main.java:22)

Answer 1

無論列表的實際大小如何，此代碼段都包含一個缺陷：

 if (i + 1 > superstarKandidaten.size()) i = 0; else i++; System.out.println(i); person2 = superstarKandidaten.get(i); 

if允許i達到super....size() ，而有效索引的范圍是0 ... super...size()-1 。

例如i=3 ， super...size()=4 3+1>4? 不， i=4 。 然后super...get(4)死亡。