What are the common causes of UnsupportedOperationException in Java?

What are the common causes of UnsupportedOperationException in Java?

The UnsupportedOperationException exception in Java is a runtime exception that usually prompts that an operation is not supported or invalid. Many developers may have encountered this exception when developing Java applications. So, what are the reasons for this exception?

1. Modification of immutable collection objects

In Java, some data structures are immutable, and their contents can only be changed by creating new objects. Such as String and Immutable Collections. When trying to modify these immutable objects, an UnsupportedOperationException is thrown.

For example, if we create an immutable List collection object:

List<Integer> list = Arrays.asList(1, 2, 3);

Then, if we try to modify it, an UnsupportedOperationException exception will be thrown:

list.remove(0); //抛出UnsupportedOperationException异常

2. Unimplemented methods

In Java, you can use abstract classes and interfaces to define some unimplemented methods, which need to be implemented by inherited or implemented subclasses. If the subclass does not implement these methods, or the implemented methods do not meet the requirements, an UnsupportedOperationException may be thrown.

For example, we define an abstract class Animal:

public abstract class Animal {
    public abstract void eat();
    public void run() {
        throw new UnsupportedOperationException("不支持run操作");
    }
}

Among them, the run method is an unimplemented method, which needs to be implemented in the subclass. However, if we do not implement the run method in the subclass, or the implemented method does not meet the requirements, an UnsupportedOperationException will be thrown.

3. Unsupported data type conversion

In Java, conversion between some data types is not supported, such as converting a String type variable into an Integer. type variable. An UnsupportedOperationException is thrown when an unsupported data type conversion is attempted.

For example, we define a variable of type String:

String s = "123";

If we try to convert it to a variable of type Integer:

Integer i = Integer.valueOf(s); //抛出UnsupportedOperationException异常

An UnsupportedOperationException will be thrown .

4. Concurrent modification exception

In Java, if multiple threads modify a collection object at the same time, it may cause concurrent modification exception. In order to avoid this exception, Java provides some synchronized collection classes, such as Vector and Hashtable. If we try to perform unsupported modification operations on these synchronized collection classes, an UnsupportedOperationException will be thrown.

For example, if we create a synchronized Vector collection object:

Vector<Integer> vector = new Vector<>();
vector.add(1);
vector.add(2);
vector.add(3);

Then, if we try to perform an unsupported modification operation on it:

for (Integer i : vector) {
    vector.remove(i); //抛出UnsupportedOperationException异常
}

will Throws UnsupportedOperationException.

Summary

UnsupportedOperationException exception usually indicates that an operation is not supported or invalid. The main reasons include modification of immutable collection objects, unimplemented methods, unsupported data type conversion and Concurrent modification exception. In order to avoid the occurrence of these exceptions, we need to be familiar with the data types and collection classes in Java, follow the Java language specifications, and use the data types and collection classes in Java correctly.

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