一、Arrays.asList()public class ListDemo { public static void main(String[] args) { String[] split = "abc,bcd,cde,def".split(","); List<String> list = Arrays.asList(split); //list.add("ggg"); list.remove("abc"); System.out.println(list); } }Convert the array to a list through Arrays.asList(), the list can only be checked and modified, and the following exceptions will be thrown when adding and deleting operations: Show We can analyze the source code:  This method returns the Arrays class inside a static inner classes java.util.Arrays.ArrayList，useless rewrite add, removemethod, and therefore will throw an exception when you call the add method. Second, through the tool class Collections.addAll()import java.util.ArrayList; import java.util.Collections; import java.util.List; public class ListDemo2 { public static void main(String[] args) { String[] split = "abc,bcd,cde,def".split(","); List< String> list = new ArrayList<String>(split.length); Collections.addAll(list,split); list.add("ggg"); list.remove("abc"); System.out.println(list); } } [bcd, cde, def, ggg]This method is the most efficient. It is converted by Collections.addAll(arrayList, strArray), a List of the same length is created according to the length of the array, and then the elements in the array are converted to binary by the Collections.addAll() method, and then added to List. It can be used when the amount of list data is large, which can increase efficiency. Third, java.util.ArrayListthe constructor usedpackage com.lzw.demo6; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class ListDemo3 { public static void main(String[] args) { String[] split = "abc,bcd,cde,def".split(","); List<String> list = new ArrayList<>(Arrays.asList(split)); list.add("ggg"); list.remove("abc"); System.out.println(list); } }This method can add, delete, and check when the amount of data is small, but it is not efficient when the amount of data is large.
The UnsupportedOperationException is one of the common exceptions that occur when we are working with some API of list implementation. It is thrown to indicate that the requested operation is not supported. This class is a member of the Java Collections Framework. All java errors implement the java.lang.Throwable interface or are inherited from another class. The hierarchy of this Exception is-
Syntax: public class UnsupportedOperationException extends RuntimeExceptionThe main reason behind the occurrence of this error is the asList method of java.util.Arrays class returns an object of an ArrayList which is nested inside the class java.util.Arrays. ArrayList extends java.util.AbstractList and it does not implement add or remove method. Thus when this method is called on the list object, it calls to add or remove method of AbstractList class which throws this exception. Moreover, the list returned by the asList method is a fixed-size list therefore it cannot be modified. The below example will result in UnsupportedOperationException as it is trying to add a new element to a fixed-size list object
Output: Exception in thread "main" java.lang.UnsupportedOperationException at java.base/java.util.AbstractList.add(AbstractList.java:153) at java.base/java.util.AbstractList.add(AbstractList.java:111) at Example.main(Example.java:14)We can solve this problem by using a mutable List that can be modified such as an ArrayList. We create a List using Arrays.asList method as we were using earlier and pass that resultant List to create a new ArrayList object.
Output Apple Banana Mango Article Tags : This example shows the possible causes of java.lang.UnsupportedOperationException. This example also shows how to fix or resolve java.lang.UnsupportedOperationException. What is java.lang.UnsupportedOperationException?java.lang.UnsupportedOperationException is thrown to denote that the requested operation is not supported by the underlying collection object. Possible causes and resolutions of the java.lang.UnsupportedOperationException1) Trying to add or remove elements from the unmodifiable list objectThe List object returned by the asList method of the Arrays class is unmodifiable. That is, you cannot change the list object structurally once it is created. Trying to add or remove elements from such a list will throw the UnsupportedOperationException exception. The Arrays#List creates a wrapper around the original array and creates a fixed-size list that cannot be modified. Thus, add and remove operations are not supported on such List object.
Output
Fix/ResolutionConvert list object returned by the asList method to an ArrayList before adding or removing elements from it like given below.
2) Trying to remove elements using an IteratorTheremove method of an Iterator class may throw the UnsupportedOperationException if the iterator is obtained from an unmodifiable List object (like given in the above example) and the remove method is called while iterating over the list.
Output
Fix/ResolutionCreate a new ArrayList or LinkedList object from the list before iterating and removing elements from the Iterator or List.
3) Trying to add, remove or set elements using ListIteratorTheadd, set, andremove methods of the ListIterator may throw UnsupportedOperationException if the ListIterator is obtained from a fixed-size List object and any of these methods are called while iterating over such a list.
Fix/ResolutionCreate a new ArrayList object from the fixed size list and get the ListIterator from ArrayList instead of a fixed size list.
4) Trying to use add or addAll methods on viewsSome methods of various collection classes return a view that is backed by the original collection and does not support add or addAll operations. One such example is the keySet method of the HashMap class. It returns a Set view of all the keys of the map that does not support add and addAll operations. If you try to call any of these methods on such a view, the code throws UnsupportedOperationException exception as given below.
Output
Fix/ResolutionAdd element/mappings to the original collection object instead of the view. Since it is just a view, the changes will be reflected in the view if you change the original collection object. Please let me know your views in the comments section below. |
