How to use List, Set, and Map collections in java

In Java, List, Set and Map are commonly used collection classes. They are all part of the Java collection framework and are used to store and manipulate a set of objects. Here's how to use them in detail:

1. List:

   • List is an ordered collection that allows storing duplicate elements.
   • Common List implementation classes include ArrayList and LinkedList.
   • Create a List object:

     List<String> list = new ArrayList<>(); // 使用ArrayList实现
     List<Integer> list = new LinkedList<>(); // 使用LinkedList实现
     

   • Commonly used methods:
     • Add elements: list.add(element), list.add(index, element),list.addAll(collection)
     • Get elements:list.get(index)
     • Modify elements:list.set(index, element)
     • Delete elements: list.remove(index),list.remove(element)
     • Determine whether the element exists:list.contains(element)
     • Get the list size:list.size()
     • Traversing a list: You can use a for-each loop or an iterator to traverse.

2. Set:

   • Set is an unordered collection and does not allow duplicate elements to be stored.
   • Common Set implementation classes include HashSet and TreeSet.
   • Create a Set object:

     Set<String> set = new HashSet<>(); // 使用HashSet实现
     Set<Integer> set = new TreeSet<>(); // 使用TreeSet实现
     

   • Commonly used methods:
     • Add elements:set.add(element)
     • Delete elements:set.remove(element)
     • Determine whether the element exists:set.contains(element)
     • Get the collection size:set.size()
     • Traversing a collection: You can use a for-each loop or an iterator to traverse.

3. Map:

   • Map is a collection of key-value pairs, each key corresponds to a value, and the key is unique.
   • Common Map implementation classes include HashMap and TreeMap.
   • Create a Map object:

     Map<String, Integer> map = new HashMap<>(); // 使用HashMap实现
     Map<String, Integer> map = new TreeMap<>(); // 使用TreeMap实现
     

   • Commonly used methods:
     • Add key-value pairs:map.put(key, value)
     • Get value:map.get(key)
     • Modify value:map.put(key, newValue)
     • Delete key-value pairs:map.remove(key)
     • Determine whether the key exists:map.containsKey(key)
     • Determine whether the value exists:map.containsValue(value)
     • Get the number of key-value pairs:map.size()
     • Traverse key-value pairs: You can use a for-each loop or iterator to traverse, or use map.entrySet()a collection of key-value pairs to traverse.