Android Training (Java article) Nineth Day-Container

2. The container is also called the collection, can store different types of elements, and the space is multiplied;

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   Distinction: Collection has no inheritance relationship with map;

   Collection Common methods:

   Size (): The capacity of the container;

   Clear (): Clears all elements in the container;

   Add (Object O): Adds any type of element;

   Remove (Object o): Removes the specified element;

   RemoveAll (Collection C): Removes the specified container;

   Contains (Object O): Determines whether a given element is contained in a container;

   
   

4. Set interface: Unordered and non-repeatable;

   What is disorder? What is the difference between disorder and randomness?

   A: The first execution of the code, the output is unordered, and once executed once, the output order will not change, unless the program is added and deleted operations;

   Disorder is limited to the first execution, random execution is not the same;

   Implementation class: HashSet, TreeSet;

   Common construction Methods: New HashSet (); New HashSet (Collection c);

   There is no extra method for set, so all of its methods are derived from the method inside the collection;

   
   

6. List interface: Ordered can be repeated

   Implementation class: ArrayList, LinkedList;

   Common methods:

   Add (Object c);

   Add (int index,object o);//Insert an element o at the specified index;

   Remove (Object o);

   Remove (int index);//If the container has an integer element, index takes precedence as the subscript index;

   Get (int index);//Return object type

   Set (int index,object o);//replaces the specified index with the specified element o the element at index;

   Size ();//container capacity;

   Clear ();//Purge

   IndexOf (Object o);//Returns the index value of the first occurrence of the specified element o in the container;

   LastIndexOf (Object o);//Returns the index value of the last occurrence of the specified element o in the container;

   
   

8. Packaging and Unpacking:

   Packaging: Converting the underlying type to an object; integer i=new integer (1);

   Unpacking: Converting an object into a basic type; int a=new Integer (1);

10. Iterator:

    Iterator: Iterates over an array or container, but unlike a loop, an iteration is traversed only once, and if there is a stop in the middle of the traversal, then the traversal proceeds from where it was last stopped, rather than starting from the beginning of the loop;

    The collection interface has the iterator () method by default;

    Common methods:

    Hasnext ();//Determine whether there are elements on the right side of the cursor;

    Next ();//Returns the object type, given the specific element value of the container, and continues to judge the next time;

    Remove ();

    
    

12. Enhanced for Loop foreach:

    Syntax: for (type variable name: Array or container name) {< output variable name can traverse;}

    Pros: Traverse extremely fast

    Disadvantage: There is no subscript, can not be used to sort, except traversal, no other method is provided;

    
    

14. Generic type:

    Why is there a generic type?

    A: Let the specified type become unique, can improve the efficiency of the Code;

    Syntax: Class name < app Type > object name =new class name < reference type > ();

    
    

16. Equals () and Hashcode () methods:

    Note: When an object exists, remember to rewrite equals () and hashcode ();

    Equals (): is only responsible for comparing the values of two objects for equality;

    Hashcode (): Determines whether two objects point to the same object (reference) and returns a hash code value;

    
    

18. Map Interface:<k,v>;

    Key cannot be duplicated;

    Implementation class: HashMap, TreeMap, Linkedhashmap;

    Common methods:

    Put (Object K,object v);

    Get (Object key);//Returns the value mapped by key

    ContainsKey (Object o);//Determines whether the given element o is contained in the container, and if so, returns true;

    Containvalue (Object o);//Determines whether the value in the container contains the given element O, and returns true if yes;

    Remove (Object o);//delete the given element;

    
    

After-school exercises:

1. Design a program to achieve 3 Chinese translation of English words based on generic map;

Code:

public class fanyi{

public static void Main (string[] args) {

HashMap m = new HashMap ();

M.put ("Apple", "Apple");

M.put ("pear", "pear");

M.put ("Orange", "orange");

For (String Str:m.keyset ()) {

System.out.println (str+ "English translation:" +m.get (str));

}

}

}

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Android Training (Java article) Nineth Day-Container