declare 2 time a variable

[brittle fractal]

/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
package shopping;

import java.util.ArrayList;

/**
 * A simple ShoppingBag
 * 
 * Stores items in an ArrayList
 * 
 * Possible to add  items
 * Also can "empty" the bag
 * 
 * You should NOT need to amend this code at all!
 * 
 * NOTE: 'Object' is the main base class for everything in Java. This means that everything 'is an' Object
 * ANy class you create will work with the shipping bag - you don't need to change this code!
 * 
 * @author Ken
 */
public class ShoppingBag {
    
    private ArrayList<Object> items;
    
    /**
     * Create a shopping bag by initialising the items to an empty arraylist
     */
    public ShoppingBag(){
        
        items = new ArrayList<Object>();
    }
    
    /**
     * Add an item to the shopping bag
     * @param someItem the item that has been bought
     */
    public void buyItem(Object someItem){
        
        this.items.add(someItem);
    }
    
 
    /**
     * create a formatted String containing all the items in the ShoppingBag
     * @return the formatted String
     * Also clears the items list -- 'empties the bag'
     */
    public String emptyBag(){
        
        String itemList = "";
        
        for(Object item: this.items){
            
            itemList = itemList + item.toString() + "\n";
        }
        
        this.items.clear();
        
        return itemList;
    }
}

guys can someone tell me why it is declare "items" to time? one is private ArrayList<Object> items; another is items = new ArrayList<Object>();. first one is just saying data type and second one run to constructer ? if it is we already also declare data type when we run the constructer, why we need to first one ?

[tough totem]

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[hushed drum]

only the first one is a declaration

it only gives the type to the variable

the second is an assignment, and an initialization in this case. it only gives the value to the variable

[brittle fractal]

but I can use the ArrayList methods without second one. why I need it ?

[hushed drum]

you can't, it only looks like you can

/run

import java.util.ArrayList;
ArrayList<Object> items;
System.out.println(items.size());

[cedar path]

@hushed drum I only received java(15.0.2) error output

file0.code.java:4: error: variable items might not have been initialized
System.out.println(items.size());
                   ^
1 error
error: compilation failed

[hushed drum]

(it's different here because these are local variables, but you get the idea)

the second one initializes the variable so it's actually usable

[brittle fractal]

but I am doing that processes at my other coding. for example :

[hushed drum]

you aren't

[hushed drum]

you don't have a = value in the declaration here

that's the difference

you need both a type and a value to get a complete, usable variable
a declaration, Type name;, only gives the type
an assignment, name = value;, only gives the value
a definition, Type name = value;, gives both

[hushed drum]

these are definitions

[hushed drum]

these are declarations and assignments

[brittle fractal]

ok I got it.

thank you so much man 😗

[tough totem]

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