Java Library Utilities Collection framework
Java Library Utilities Collection framework
Overview:
The Utilities Collection framework in the Java class library provides a powerful and flexible tool for processing and operating collection data.In addition to the basic collection classes such as List, SET, and Map, Utilities Collection also provides a series of practical classes and methods to enhance the function of collection.This article will explore the advanced function of how to use the Utilities Collection framework and provide some Java code examples.
Non -empty set treatment:
In actual development, we often need to handle non -empty sets containing elements.The Utilities Collection framework provides an elegant way to deal with this situation, even if the `CollectionUtils.ISNOTEMPTY" method is used.This method accepts a collection as a parameter and returns a Boolean value to indicate whether the set is empty.The following is an example:
import org.apache.commons.collections4.CollectionUtils;
List<String> list = Arrays.asList("apple", "banana", "orange");
if (CollectionUtils.isNotEmpty(list)) {
// The processing logic of the time when collecting non -empty
System.out.println ("collection non -empty");
} else {
// The process of processing when the collection is empty
System.out.println ("collection as empty");
}
In the above examples, if the collection list contains elements, it will output "collection non -empty"; if the set is empty, the "collection is empty" will be output.
Collection filter:
The Utilities Collection framework provides a convenient way to filter the elements in the collection, even if the `CollectionUtils.Filter` method is used.This method accepts a collection and a predict as a parameter, and returns a filtering collection.The following is an example:
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.Predicate;
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
CollectionUtils.filter(numbers, new Predicate<Integer>() {
@Override
public boolean evaluate(Integer number) {
return number % 2 == 0;
}
});
System.out.println(numbers);
In the above example, we define a predicate to filter the even number in the collection.By calling the `CollectionUtils.filter` method, we can get a new collection containing only the even number.The output result is `[2, 4]`.
Type conversion:
The Utilities Collection framework provides a simple way to convert the element type in the set, even if the `CollectionUtils.Collect` method is used.This method accepts a collection, a transformer, and a target set class as a parameter, and returns a converted set.The following is an example:
import org.apache.commons.collections4.CollectionUtils;
import org.apache.commons.collections4.Transformer;
List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5);
Set<String> stringNumbers = new HashSet<>();
CollectionUtils.collect(numbers, new Transformer<Integer, String>() {
@Override
public String transform(Integer number) {
return String.valueOf(number);
}
}, stringNumbers);
System.out.println(stringNumbers);
In the above example, we define a converter to convert the integer in the set to a string.By calling the `CollectionUtils.Collet` method, we can get a new set composed of string.The output result is `[1, 2, 3, 4, 5]`.
Summarize:
By using the advanced function of the Utilities Collection framework, we can easily process and operate collecting data.This article introduces several common functions such as non -air collection processing, set filtering and type conversion, and provides corresponding Java code examples.Hope this article can provide some help when you use the Java class library Utilities Collection framework.
