Please help , JAVA, class with This. Its will take some time, so please..

[keavlar]

Hey guys, i took a code we were suppose to write down in school. But i dont really get the [This] in the code, why it was used like that ?i mean i will write all the code, i will be more then appreciate if you could to explain me. I  mark the parts that i am not sure i understand, i mean , why in all parts we had to use getThis.

 

I really ppreciate if you could take few min to look on that and explain,. 

THANK YOU

 

 

 

.CODE [public class Box{
    
    private int _width;
    private int _length;
    private int _height;
    
    private final int DEFAULT_WIDTH = 10;
    private final int DEFAULT_LENGTH = 10;
    private final int DEFAULT_HEIGHT = 10;
    
    public Box () {
        _width = DEFAULT_WIDTH;
        _length = DEFAULT_LENGTH;
        _height = DEFAULT_HEIGHT;
    }
    
    public Box (int val){
        if (val <=0){
            _width = DEFAULT_WIDTH;
            _length = DEFAULT_LENGTH;
            _height = DEFAULT_HEIGHT;
        }
        
        else {
            _width = val;
            _length = val;
            _height = val;
        }
    }
    
    public Box (int length, int height, int width){
        if (width<=0) 
            _width = DEFAULT_WIDTH;
        else 
            _width = width;
            
        if (length<=0) 
            _length = DEFAULT_LENGTH;
        else 
            _length = length;
            
        if (height<=0) 
            _height = DEFAULT_HEIGHT;
        else 
            _height = height;
    }
        
    public void setLength (int val){
        if (val>0) 
            _length = val;
    }
        
    public void setHeight (int val){
        if (val>0)  
            _height = val; 
     }
     
    public void setWidth (int val){
        if (val>0) 
            _width = val;
    }
    
    public int getLength(){
        return _length;
    }
    
    public int getHeight(){
        return _height;
    }
    
     public int getWidth(){
        return _width;
    }
        
    public void resize (int factor) {
        if (factor >0){
            _width = this.getWidth()*factor; ;
            _length = this.getLength()*factor;
            _height = this.getHeight()*factor;
        }
    }
    
    public void resizeToLength() {
       int change = this.getLength();
       _width = change;
       _height = change;
    }
        
     public void resizeToHeight() {
        int change = this.getHeight();
        _width = change;
        _length = change;
    }   
    
     public void resizeToWidth() {
        int change = this.getWidth();
        _height = change;
        _length = change;
    }   
    
    public int volume(){
        return this.getHeight()*this.getWidth()*this.getLength();
    }
    
     public int surfaceArea(){
        return 2*((this.getHeight() * this.getWidth())+(this.getHeight() * this.getLength())+(this.getWidth() * this.getLength())) ;
    }
 }    ]

 

 

SECOND PART TO TEST THE CLASS

[import java.util.Scanner;
public class Driver{
    public static void main(String[]args) {
        
        Scanner scan = new Scanner(System.in);
        
        Box boxy1 = new Box ();
        
        System.out.println("boxy1- length: "+ boxy1.getLength() + 
        " height: " +  boxy1.getHeight() + " width: " + boxy1.getWidth());
        
        boxy1.resize(3);
        int volumeBoxy1 = boxy1.volume();
        int surfaceAreaBoxy1 = boxy1.surfaceArea();
        
        System.out.println("boxy1- volume: " + volumeBoxy1 +
        " surface area: " + surfaceAreaBoxy1);
        
        System.out.println("Please enter 3 positive numbers for length, height and width");
        int length = scan.nextInt();
        int height = scan.nextInt();
        int width = scan.nextInt();
        
        Box boxy2 = new Box (length, height, width); 
        
        int volumeBoxy2 = boxy2.volume();
        int surfaceAreaBoxy2 = boxy2.surfaceArea();
        
        System.out.println("boxy2- volume: " + volumeBoxy2 +
        " surface area: " + surfaceAreaBoxy2);
        
        boxy2.resizeToHeight();
        int volumeBoxy2AferChange = boxy2.volume();
        int surfaceAreaBoxy2AferChange = boxy2.surfaceArea();
        
        System.out.println("boxy2- length: "+ boxy2.getLength() + 
        " height: " +  boxy2.getHeight() + " width: " + boxy2.getWidth() +
        " volume: " + volumeBoxy2AferChange + " surface area: " +
        surfaceAreaBoxy2AferChange);
        
    }
}
        ]

 

[VinsinityKT]

this is basically the name of the object who's values is associated with it. If you want a more detailed explanation I'll try, just I should be sleeping now.  In terms of width, length and height, you are getting the values from "this". So which value of width, length or height you want? You want the ones from "this". Sorry if I didn't use proper terms. 

[keavlar]

1 minute ago, VinsinityKT said:

this is basically the name of the object who's values is associated with it. If you want a more detailed explanation I'll try, just I should be sleeping now.  In terms of width, length and height, you are getting the values from "this". So which value of width, length or height you want? You want the ones from "this". Sorry if I didn't use proper terms. 

Thx for your time first of all, sec. , i am not sure, i mean, we were told to multiply the size of the cube sides by 3 , as you can see in driver, but i donr really understand why , the sides were took from this.getHeight and so , i mean, there is no value from were it was taken.  

[trag1c]

The this keyword is for accessing members of the object in which they belong to. In your case it would be an instance of the box class.

 

I don't know Java but I just prefer to prefix my variables with m_ for member as writing this-> (or this. in java's case) just gets annoying and causes clutter IMO.

 

[keavlar]

1 minute ago, trag1c said:

The this keyword is for accessing members of the object in which they belong to. In your case it would be an instance of the box class.

 

I don't know Java but I just prefer to prefix my variables with m_ for member as writing this-> (or this. in java's case) just gets annoying and causes clutter IMO.

 

We mast use THIS in this one 

[Sketched360]

Okay lets make an example of a classroom. Say the class (Java Class) is the classroom A1 and you are a property in the classroom. Say i declare you as " public string student = 'keavlar ' " . So while we are inside this class A1, i can refer to where you are as " this " classroom. Since we all know where " this " is, so in programmatic sense it would be " this.student ". Whereas if i was in a classroom, say C5 and someone asks me where you are, i can't say " this " classroom since you, the property of class A1 is not in C5. I would have to tell them where you are exactly so i would say " He is in classroom A1 ". Which in programmatic terms you say, " Classroom ClassA1 = new Classroom(); " then saying, " ClassA1.student ".

 

I hope this helps. Let me know if you were confused or need help understanding it 

[keavlar]

24 minutes ago, Sketched360 said:

Okay lets make an example of a classroom. Say the class (Java Class) is the classroom A1 and you are a property in the classroom. Say i declare you as " public string student = 'keavlar ' " . So while we are inside this class A1, i can refer to where you are as " this " classroom. Since we all know where " this " is, so in programmatic sense it would be " this.student ". Whereas if i was in a classroom, say C5 and someone asks me where you are, i can't say " this " classroom since you, the property of class A1 is not in C5. I would have to tell them where you are exactly so i would say " He is in classroom A1 ". Which in programmatic terms you say, " Classroom ClassA1 = new Classroom(); " then saying, " ClassA1.student ".

 

I hope this helps. Let me know if you were confused or need help understanding it 

not sure, you get what i dont understand , 

in  public void resize (int factor)

_width = this.getWidth()*factor;

 

so meaning it will take teh value from 

public getWidth()

return _width ; 

 

and there is no value here. 

 

I want to understand the part of why this,getWidth .  

 

 

 

[Sketched360]

5 minutes ago, keavlar said:

not sure, you get what i dont understand , 

in  public void resize (int factor)

_width = this.getWidth()*factor;

 

so meaning it will take teh value from 

public getWidth()

return _width ; 

 

and there is no value here. 

 

I want to understand the part of why this,getWidth .  

 

 

 

 

Okay, so yes this.getWidth() will take the value of 

public getWidth()

return _width ; 

 

I can't really help if i'm not sure what to help with  

So do you need to know the reason why the " this.getWidth() " is being used??

or

is it that it does not have a value?

[FRN]

"this" is a keyword in Java. It simply means the current object. You might want to use standard naming convention for variables which is camelCaseNotation (this is just me nitpicking)

[Lucaz97]

So... You are gonna use the method like this:

 

myBox.resize(3);

 

it will take your box height length and height, multiply it by 3 and assign the new values to the variables

 

the this.getWidth() is the method getWidth()called with the object you called at the beginning, in this case, myBox. That will return the value of the width of the object myBox.

 

hope I got what you were asking for, if is not the case, try to explain better what s the part you don't get...