Java Intermediate--Set frame "1"

Set Frame ----ArrayList

Introduction: Let's take a look at the use of traditional arrays

2. write a hero object class

   package  cn.jse.t1;

   public  , class  hero {

   public  string Name;

   public   float  hp;

   public   int  damage;

    

   public  hero () {}

   //Add a constructor to initialize name

   public  hero (String name) {

   this . Name=name;

   }

   //Override a ToString method

   public  string toString () {

   return  name;

   }

   }

4. Write a test class

   Package cn.jse.t1;

   Public class testcollection {

   Public Static void Main (string[] args) {

   Limitations of arrays

   Hero hero[] = new hero[10];

   Analysis: Declared an array of length 10, if not finished is a waste of memory, more than 10 and not fit

   Hero[0] = new Hero ("ADC");

   hero[11]= new Hero ("Mid"); There's more than 10 here and there will be an error.

   }

   }

5. in order to solve this embarrassing situation, we can use the container class ArrayList, We add some code inside the test class.

   Package cn.jse.t1;

   import java.util.ArrayList;

   Public class testcollection {

   Public Static void Main (string[] args) {

   ...

   In order to solve the limitation of array, the concept of container class is introduced.

   ArrayList heros=new ArrayList();

   heros . Add (new Hero ("single"));

   Output the capacity of the current container

   System. out. println (Heros.size ());

   heros . Add (new Hero ("aux"));

   System. out. println (Heros.size ());

   The result is that the capacity of the container increases with the increase of the object, and the boundary problem of the array is not considered.

   }

   }

   We can look at the output of the console:

   1

   2

6. we can take a look . Common methods of ArrayList:

   How to use: We also add new code (add,contains) to the test class

   Package cn.jse.t1;

   import java.util.ArrayList;

   Public class testcollection {

   Public Static void Main (string[] args) {

   ...

   Next we can look at the common methods of ArrayList

   arraylistNew arraylist

   Put five objects into a ArrayList

   for (int i=0;i<5;i++) {

   Heros2.add (new Hero ("Hero" + i));

   }

   System. out. println (heros);

   Add an object at the specified position such as in Subscript 3 position add a superhero

   Hero superhero = new Hero ("Super Hero");

   Heros2.add (3, superhero);

   Outputs all the hero in the array

   System. out. println (Heros2.tostring ());

   Determine whether an object is in a container by means of contains

   System.  out. println ("Then this Hero6 is not here?") The answer is: "+heros2.contains (new Hero (" Hero6 "));

   System.  out. println ("then this superhero is not here?") The answer is: "+heros2.contains (superhero));

   }

   }

   Console output:

   [Middle order, auxiliary]// This is because we have added 2 hero

   [Hero 0, Hero 1, Hero 2, Super hero, Hero 3, Hero 4]

   so this  Hero6 's not here? The answer is: false

   so this superhero is not here? The answer is: true

   Other methods are not listed, interested students can look at the relevant knowledge points

Java Intermediate--Set frame "1"