The collection processing of Ka Commons Collections framework in the Java Class Library
The collection processing of Ka Commons Collections framework in the Java Class Library
Overview:
Ka Commons Collections is part of the Apache Commons Collection. It provides a powerful and flexible tool for handling the Java collection.It contains many practical classes and interfaces, which can perform various operations and conversions on the set, making the collection processing simpler and efficient.
1. Collection class:
1. BAG: BAG is a collection similar to Set, but allows elements to repeat.It provides a series of methods to count the number of elements. For example, the GetCount (Object) method can return the number of times the specified element appears.
Example code:
// Create a BAG object
Bag<String> bag = new HashBag<>();
// Add elements to BAG
bag.add("apple");
bag.add("banana");
bag.add("apple");
bag.add("orange");
// The number of statistical elements
System.out.println ("Number of Apple:" + Bag.getCount ("Apple");
System.out.println ("Number of Banana:" + BAG.GetCount ("Banana");
System.out.println ("Number of Orange:" + Bag.getCount ("Orange");
2. Listutils: Listutils provides a series of static methods for various operations for List.For example, the Reverse (List) method can reverse the elements in the list.
Example code:
// Create a list object
List<String> list = new ArrayList<>();
list.add("apple");
list.add("banana");
list.add("orange");
// Reverse elements in List
ListUtils.reverse(list);
// Output the element order after reversing
for (String item : list) {
System.out.println(item);
}
3. PredicateUtils: Predicateutils provides a series of static methods for filtering elements in the collection.For example, the selection (Collection, Predicate) method can select the conditional elements from the set according to the predicate conditions.
Example code:
// Create a list object
List<String> list = new ArrayList<>();
list.add("apple");
list.add("banana");
list.add("orange");
// Elements that start with letter A in the filter collection
CollectionUtils.select(list, new Predicate<String>() {
@Override
public boolean evaluate(String item) {
return item.startsWith("a");
}
});
// Output Eligible elements
for (String item : list) {
System.out.println(item);
}
2. Collection interface:
1. Predicate: Predicate is a functional interface that defines the Evaluate (T) method to determine whether a certain object meets specific conditions.You can create a custom predicate by implementing the Predicate interface.
Example code:
// Create an object of the predicate that is used to determine whether the string is empty
Predicate<String> isEmpty = new Predicate<String>() {
@Override
public boolean evaluate(String item) {
return item.isEmpty();
}
};
// Judging whether the string is empty
System.out.println (isempty.evaluate (""); // output true
System.out.println (Isempty.evaluate ("Hello"); // Output false
2. Transformer: Transformer is a functional interface that defines the transform (t) method for the conversion of the object.You can create a custom converter by implementing the Transformer interface.
Example code:
// Create a converter object to convert the string into a capitalized
Transformer<String, String> toUpperCase = new Transformer<String, String>() {
@Override
public String transform(String item) {
return item.toUpperCase();
}
};
// Convert strings to uppercase
System.out.println(toUpperCase.transform("hello")); // 输出HELLO
System.out.println(toUpperCase.transform("world")); // 输出WORLD
in conclusion:
The Ka Commons CollectionS framework provides rich functions and flexible interfaces, which is convenient for Java developers to handle the collection.By using a collection class and interface, we can easily implement the operation of collections, conversion, and filtering.These functions make the collection process more simple and efficient, providing developers with a better programming experience.
