Exception in thread "main" java.lang.IndexOutOfBoundsException: Index 4 out-of-bounds for length 4	at java.base/jdk.internal.util.Preconditions.outOfBounds(Unknown Source)	at java.base/jdk.internal.util.Preconditions.outOfBoundsCheckIndex(Unknown Source)	at java.base/jdk.internal.util.Preconditions.checkIndex(Unknown Source)	at java.base/java.util.Objects.checkIndex(Unknown Source)	at java.base/java.util.ArrayList.get(Unknown Source)	at imooc_collection_map_demo/com.imooc.collection.SetTest.testAdd(SetTest.java:34)	at imooc_collection_map_demo/com.imooc.collection.SetTest.main(SetTest.java:58)