java ArrayList索引超出范围,但实际上没有?
因此,我的java代码现在有一个非常令人困惑的bug。我只想插入代码的重要部分,并解释它应该做什么:
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)
现在,下面的代码看起来有点奇怪,它基本上应该读取两个不同的supermarkandedaten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);
}
我不打算编写代码的其余部分,因为这是不必要的,以下是输出:
{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)
# 1 楼答案
无论列表的实际大小如何,此代码段都包含一个缺陷:
if
允许i
达到super....size()
,而有效指数在0
范围内super...size()-1
例如
i=3
,super...size()=4
,3+1>4?
不,i=4
。然后super...get(4)
死亡