Java: How to parse Double into Int?

[Hip]

Hey guys,

 

I have written a code where I put in a double and then convert the double into a Integer. But this somehow does not work.

Can you tell me how to solve this?

 

import javax.swing.*;

public class Test
{
	public static void main(String[] args)
    {
    	double inputDouble;
        int convertedFromDouble;
        
        inputDouble = Double.parseDouble(JOptionPane.showInputDialog(null, "Put in a Double"));
        
        convertedFromDouble = Integer.parseInt(inputDouble);
        
        JOptionPane.showMessageDialog(null, "Your Double is "+inputDouble);
        JOptionPane.showMessageDialog(null, "Your Int ist "+convertedFromDouble);
        System.exit(0);
    }
}

 

[Adorable Cat]

Couldn't you just cast the double to an int, like

int convertedFromDouble = (int)inputDouble;

 

[Hip]

Just now, Adorable Cat said:

Couldn't you just cast the double to an int, like

int convertedFromDouble = (int)inputDouble;

 

Isn't this also possible with parse somehow? Thanks for your help

[reniat]

Integer.parseInt() is for strings. You can just use (int) as @Adorable Cat mentioned

[Hip]

12 minutes ago, reniat said:

Integer.parseInt() is for strings. You can just use (int) as @Adorable Cat mentioned

So String to Double, String to float or String to Int = parse? And Double to Int or float to int = (type) X ?

[reniat]

19 minutes ago, Hip said:

So String to Double, String to float or String to Int = parse? And Double to Int or float to int = (type) X ?

Yes kind of, but think about it less like "when casting I use ____ for this type", remember that parse is a method on Integer (or Double, or Float). 

This syntax:

NewType someValue = (NewType) oldValue;

is the only way to cast that's built directly into the language. The parse methods on Float, Integer, and Double are just methods used to make objects of those types given other data. They aren't "casting" so much as they are almost like static constructors, where you give it a double and it gives you a new Integer object. parse could also be renamed Integer.createFromString(String s); and it'd mean the same thing.

 

The difference is that casting is simply changing the reference to the object, while methods like these parse methods aren't as limited by the original. For example, you could make a parse method that had custom logic, like:
 

static int parsePositive(double d) {
    return (d < 0) ? 0 : (int) d;
}

// or if you're not familiar with ternaries:
static int parsePositive(double d) {
    if (d < 0) {
        return 0;
    }
    return (int) d; 
}

 

And raw casting as built by the language doesn't provide that level of customization, because it's simply changing reference types.

 

So while yes, casting does let you take an object of one type and create an object of a different type from that same object, i would not call it accurate to say that parse() is "casting" here, as there is no valid general transformation from string to numeric (which is why you can't just use the normal cast), though this probably just down to semantics.

[Hip]

35 minutes ago, reniat said:

Yes kind of, but think about it less like "when casting I use ____ for this type", remember that parse is a method on Integer (or Double, or Float). 

This syntax:

NewType someValue = (NewType) oldValue;

is the only way to cast that's built directly into the language. The parse methods on Float, Integer, and Double are just methods used to make objects of those types given other data. They aren't "casting" so much as they are almost like static constructors, where you give it a double and it gives you a new Integer object. parse could also be renamed Integer.createFromString(String s); and it'd mean the same thing.

 

The difference is that casting is simply changing the reference to the object, while methods like these parse methods aren't as limited by the original. For example, you could make a parse method that had custom logic, like:
 

static int parsePositive(double d) {
    return (d < 0) ? 0 : (int) d;
}

// or if you're not familiar with ternaries:
static int parsePositive(double d) {
    if (d < 0) {
        return 0;
    }
    return (int) d; 
}

 

And raw casting as built by the language doesn't provide that level of customization, because it's simply changing reference types.

 

So while yes, casting does let you take an object of one type and create an object of a different type from that same object, i would not call it accurate to say that parse() is "casting" here, as there is no valid general transformation from string to numeric (which is why you can't just use the normal cast), though this probably just down to semantics.

 

Ok that's a kinda complicated explanation to me because I don't know that much yet lol

I tried Integer.createFromString(String s) and it didn't work for me somehow.

[reniat]

31 minutes ago, Hip said:

and it didn't work for me somehow.

Sorry I may have over-explained a bit. Integer.createFromString() was an example I made up, illustrating that .parse() is just another method, not something baked into the language like casting using parenthesis like (int)

[Hip]

22 minutes ago, reniat said:

Sorry I may have over-explained a bit. Integer.createFromString() was an example I made up, illustrating that .parse() is just another method, not something baked into the language like casting using parenthesis like (int)

Now I understand thanks.

Can you answer me another question, I want to print something in System.our.println and somehow I get errors like "error: ';' expected" "error: not a statement" and " error: ')' expected"

 

This is the outprint:

 System.out.println("double: "+doubleWert"\nbyte: "+byteWert);

 

It only occures when I put in \n

 

I solved it with:

System.out.println("double: "+doubleWert+"\n"+"byte: "+byteWert);

 

[Guest]

On 4/22/2019 at 10:06 AM, Adorable Cat said:

Couldn't you just cast the double to an int, like

int convertedFromDouble = (int)inputDouble;

 

This is my favourite (because ease) method but... if the double has a value like 10.5 wouldn’t that cause an issue? Or would the parsing drop the decimal? 

[Hip]

56 minutes ago, fpo said:

This is my favourite (because ease) method but... if the double has a value like 10.5 wouldn’t that cause an issue? Or would the parsing drop the decimal? 

double 10.5 would convert to int 10