In -depth analysis of the collection class in the core framework of Java
In -depth analysis of the collection class in the core framework of Java
Overview:
The core framework of Java provides a wealth of collection classes for storage and operation objects.These collection classes provide us with a convenient and efficient way to process data. The function and performance of the collection class directly affect the efficiency and scalability of the application.This article will in -depth analysis of the collection classes in the core framework of the Java, introduce the characteristics and usage of various collection classes in detail, and provide the corresponding Java code example.
1. List collection class:
List is one of the most basic collection categories in Java and is used to store a set of orderly elements.List allows duplicate elements and can access elements in the set in the sequence of insertion.Java provides a variety of classes that implement List interfaces, such as ArrayList, LinkedList, and Vector.Below is an example code using ArrayList:
import java.util.ArrayList;
import java.util.List;
public class ListExample {
public static void main(String[] args) {
List<String> list = new ArrayList<>();
// Add elements
list.add("Java");
list.add("Python");
list.add("C++");
// Visit elements
System.out.println (list.get (0)); // Output: java
// Delete elements
list.remove (1); // Delete python
// Traversing elements
for (String element : list) {
System.out.println(element);
}
}
}
2. SET collection class:
Set is a collection class used in Java to store non -repeated elements.SET does not guarantee the order of elements and cannot access elements through indexes.Java provides a variety of classes that implement SET interfaces, such as HashSet, TreeSet, and LinkedhashSet.Below is an example code using HashSet:
import java.util.HashSet;
import java.util.Set;
public class SetExample {
public static void main(String[] args) {
Set<String> set = new HashSet<>();
// Add elements
set.add("Java");
set.add("Python");
set.add("C++");
set.add ("java"); // Repeated elements will not be added
// Traversing elements
for (String element : set) {
System.out.println(element);
}
// Determine whether the element exists
System.out.println (set.contains ("java"); // Output: true: true
// Delete elements
set.remove("Python");
// Number of elements
System.out.println (set.size ()); // Output: 2
}
}
3. MAP collection class:
MAP is a collection class used in Java to store key values pairs.Each key value pair is an Entry object, which can access the corresponding value through the key.Java provides a variety of categories that implement MAP interfaces, such as HashMap, TreeMap, and LinkedhashMap.Below is an example code using HashMap:
import java.util.HashMap;
import java.util.Map;
public class MapExample {
public static void main(String[] args) {
Map<String, Integer> map = new HashMap<>();
// Add key value pair
map.put("Java", 1);
map.put("Python", 2);
map.put("C++", 3);
// Access value
System.out.println (map.get ("java"); // Output: 1
// Traversing key value pair
for (Map.Entry<String, Integer> entry : map.entrySet()) {
System.out.println(entry.getKey() + ": " + entry.getValue());
}
// Judging whether the key exists
System.out.println (Map.Containskey ("Python"); // Output: TRUE
// Delete the key value pair
map.remove("C++");
// Key value pair
System.out.println (map.size ()); // Output: 2
}
}
in conclusion:
The collection class in the Java core framework provides rich functions and flexible usage, which is suitable for various application scenarios.By in -depth understanding of the characteristics and use of the collection class, we can handle and operate data more efficiently.When developing Java applications, reasonable selection and use of the collection class will help us improve the quality and performance of code.
