Go Java Object Container

Use Java to implement Notepad functionality. Start by listing the features that Notepad requires:

1. You can add records (strings);
2. The number of record bars can be obtained;
3. One of the records can be deleted;
4. A record of the specified section may be obtained;
5. You can list all the records.

If this notepad is part of a large program, that is, a top-level program, then the upper-level program may invoke one of the data listed above in this Notepad.

So we call the above listed functions as the interface of this notepad.

Then calling these interfaces is the public function (method) of this class through Notepad.

But how do you make a record? It is clear that the recorded string cannot be recorded in an array because the length of the array is pre-set. This is a generic container arraylist<> , this Arraylist is also a class of the system, so when using it to define a new object to come out: private arraylist<string>  Notes = new arraylist<string> (); also declare import java.util.ArrayList;

ArrayList can be arbitrarily stored in the data, unlimited number, which realizes the requirements of Notepad.

Basic operations for Arraylist: arraylist<string> notes

• Notes.add ()
• Notes.size ()
• Notes.remove (Index)
• Notes.get (Index)
• Notes.toarray (string[] a=new string[notes.size ()])

The interface function of Notepad is implemented by the above operation.

1PackageNotebook23ImportJava.util.ArrayList;45PublicClassNotebook {67Private arraylist<string> notes =New arraylist<string>();89PublicvoidAdd (String s) {10Notes.add (s);11}1213PublicIntGetSize () {14ReturnNotes.size ();15}1617Publicvoid Removenote (IntIndex) {18Notes.remove (index);19}2021stPublic String Getnote (IntIndex) {22ReturnNotes.get (index);23}2425PublicString[] List () {String[] A =NewString[notes.size ()];27Notes.toarray (a);28ReturnA29}3031PublicStaticvoid Main (string[] args) {//TestNotebook NB =new Notebook ();  Nb.add ("frist"  System.out.println (Nb.getsize ());  String[] A = Nb.list () for38 Span style= "color: #000000;" > System.out.println (s); 39 }40 }41 42}       

Notebook.java

Run:

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In addition, the container type also has a collection container (set), such as HashSet, is also a class, has the attribute is the inner element is unordered, cannot have the duplicate element, and the Mathematics collection concept is identical.

You can see the difference between the two containers, ArrayList and HashSet, from the results of the program running.

Note: The program can also see that the output of two containers is no longer assigning each element of the container to another array, and then outputting each element in the array through a For Each loop. Here we are directly println out of the object of a container, is possible. This is because: {

As shown in the first red box, if there is a "publicString toString () {}" function in a class, you can directly println the object name of the class, and the output will automatically call the ToString function, as shown in the Second red box. So, we suspect that there must also be a function like "public String toString () {}" in the two common source files of ArrayList and HashSet .

}

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hashmap Container: hashmap<key,value>

A key corresponding to a value, when given a key multiple put, the key corresponds to the last put value, (one input denomination, output multi-dollar name of the program, such as: 1 cents is called 1penny. ）

Traversal of HashMap:

Go Java Object Container