How to fix: Java Collection Error: Collection operation exception

How to solve: Java collection error: Collection operation exception

Introduction:
In the development process of Java, collections are often used to store and operate a group of data. However, sometimes we encounter collection operation exceptions, which may cause the program to crash or produce incorrect results. This article will introduce some common collection operation exceptions and provide corresponding solutions and code examples.

I. Types and causes of collection operation exceptions:

1. ConcurrentModificationException (concurrent modification exception):
   This exception usually occurs during the process of using an iterator to traverse a collection. This exception will be thrown when the program modifies the collection (adds, deletes, modifies elements, etc.) while iterating the collection.
2. UnsupportedOperationException (unsupported operation exception):
   This exception occurs when the program calls an operation that is not supported by the collection, such as modifying a read-only collection.

II. Solution:

1. Solution to concurrent modification exception:
   a. Use Iterator's remove() method to delete elements instead of using it directly The remove() method of the collection.
   b. Use concurrency-safe collection classes (such as ConcurrentHashMap, CopyOnWriteArrayList) instead of ordinary collection classes.
   c. While traversing the collection, avoid adding, deleting, and modifying elements to the collection.

The following is a simple sample code to demonstrate the solution to the concurrent modification exception:

List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");

Iterator<String> iterator = list.iterator();
while(iterator.hasNext()){
    String element = iterator.next();
    if(element.equals("B")){
        iterator.remove();
    }
}

2. The solution to the unsupported operation exception:
   a. Before using a collection, first check whether the collection supports the corresponding operations, which can be determined through Collection's isAddSupported(), isRemoveSupported() and other methods.
   b. Use collection classes that support corresponding operations to replace unsupported collection classes.

The following is a simple sample code to demonstrate the solution to unsupported operation exceptions:

List<String> list = new ArrayList<>();
list.add("A");
list.add("B");
list.add("C");

if(list instanceof RandomAccess){
    list.add(1, "D");
}else{
    List<String> newList = new ArrayList<>();
    for(int i=0; i<list.size(); i++){
        if(i == 1){
           newList.add("D");
        }
        newList.add(list.get(i));
    }
    list = newList;
}

Conclusion:
In Java collection operations, avoid concurrent modification exceptions and unsupported operation exceptions are issues that must be paid attention to during the development process. By understanding the types and causes of exceptions and taking corresponding solutions, the stability and correctness of the program can be ensured. I hope the solutions provided in this article can be helpful in solving the problem of collection operation exceptions.

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