Complex Numbers

**TmDee** · February 24th, 2019, 11:12 AM

public class ComplexGet {
	private double re, im;
 
	public ComplexGet(double reëel, double imag) {
		re = reëel;
		im = imag;
	}
 
	public double real() {
		return re;
	}
 
	public double imaginair() {
		return im;
	}
 
	public void optellen(ComplexGet y) {
		re = re + y.real();
		im = im + y.imaginair();
 
	}
 
	public void vermenigvuldigen(ComplexGet y) {
 
		re = ((re * y.real()) - (im * y.imaginair()));
		im = ((re * y.imaginair()) + (im * y.real()));
 
	}
 
	public void inverteren(ComplexGet x) {
		re = (x.real() / (x.real() * x.real()) + (x.imaginair() * x.imaginair()));
		im = (x.imaginair() / (x.real() * x.real()) + (x.imaginair() * x.imaginair()));
	}
 
}

public class main {
 
	public static void main(String[] args) {
		ComplexGet getal1 = new ComplexGet(1.0, 2.0);
		ComplexGet getal2 = new ComplexGet(3.0, 4.0);
		ComplexGet temp = getal1;
		ComplexGet temp2= getal1;
		ComplexGet temp3= getal1;
		temp.optellen(getal2);
		System.out.printf("Som = %.1f + %.1fi"+"\n", temp.real(), temp.imaginair());
		temp2.vermenigvuldigen(getal2);
		System.out.printf("Vermenigvuldiging = %.1f + %.1fi"+"\n", temp2.real(), temp2.imaginair());
		temp3.inverteren(getal1);
		System.out.printf("Inverteren = %.1f + %.1fi", temp3.real(), temp3.imaginair());
 
 
 
	}
 
}

After the first "optellen" that means counting up the 2 numbers are counted up works fine. But then for "vermenigvuldigen", multiplication it takes the complex number of the som and getal2. And it should be getal1 and getal2 not the numbers from the som. Any help?

**Norm** · February 24th, 2019, 12:04 PM

Can you copy the contents of the console from the program's execution and paste it here?
Add some comments saying what is wrong and show what the desired output is.

**jim829** · February 24th, 2019, 01:29 PM

Not certain if this is the problem but the following code simply assigns temp, temp2, and temp3 the same reference. So if you make a change in one, the others are affected too.

ComplexGet temp = getal1;
ComplexGet temp2= getal1;
ComplexGet temp3= getal1;

Regards,
Jim

**TmDee** · February 24th, 2019, 03:46 PM

Originally Posted by Norm

Can you copy the contents of the console from the program's execution and paste it here?
Add some comments saying what is wrong and show what the desired output is.

Knipsel.jpg
Console says for "optellen 4.0+6.0i. <-- this is correct.
for "vermenigvuldigen" : -12.0 + -30.0i
for "inverteren" : 899.9 + 900.0i

For multiplication, "vermenigvuldigen" the answer should be: 5.0 + 12i.
It's wrong because he uses the (4.0 + 6.0i) to multiplicate with (3.0,4.0) and he should use (1.0,2.0) * (3.0,4.0) by the formula that is with "vermenigvuldigen".
Same happens for 1/complex number . It should be 0.2 + -0.4i.

Thanks in advance

**TmDee** · February 24th, 2019, 03:47 PM

Originally Posted by jim829

Not certain if this is the problem but the following code simply assigns temp, temp2, and temp3 the same reference. So if you make a change in one, the others are affected too.

ComplexGet temp = getal1;
ComplexGet temp2= getal1;
ComplexGet temp3= getal1;

Regards,
Jim

Yeah saw that now too, thanks Jim!

**Norm** · February 24th, 2019, 04:16 PM

Please don't post images. The posted image is too small to read and text can not be copied from an image for including in a response.

What is the results after you corrected the problem that Jim pointed out?

**TmDee** · February 24th, 2019, 05:07 PM

Yeah well I saw that so i posted the answers of the console under the image and it just didn't make any difference by clearing those commands that Jim told me.

**Norm** · February 24th, 2019, 05:22 PM

it just didn't make any difference by clearing those commands that Jim told me.

Can you post the new code that shows the changes you made?
Also copy the contents of the console from when you execute the program and paste it here.

A suggestion: Make the class immutable. Make the re and im variables final and have the computation methods return a new instance of the class.

**TmDee** · February 25th, 2019, 10:57 AM

Originally Posted by Norm

Can you post the new code that shows the changes you made?
Also copy the contents of the console from when you execute the program and paste it here.

A suggestion: Make the class immutable. Make the re and im variables final and have the computation methods return a new instance of the class.

Som = 4,0 + 6,0i
Vermenigvuldiging = -12,0 + -30,0i
Inverteren = 899,9 + 900,0i

This is the console log and it should be by "vermenigvuldigen" -5 + 12i.

And your suggestion I don't really understand I'm just a beginner in Oriented and object programming I'm 18 and it's I only had like 3 weeks lessons about it

**jim829** · February 25th, 2019, 11:22 AM

A subtle error I believe.

re = ((re * y.real()) - (im * y.imaginair())); <----- re here is the current re
im = ((re * y.imaginair()) + (im * y.real())); <---- re here is the just modified re which is not what you want.

Regards,
Jim

**TmDee** · February 25th, 2019, 12:07 PM

public class main {
 
	public static void main(String[] args) {
		ComplexGet getal1 = new ComplexGet(1.0, 2.0);
		ComplexGet getal2 = new ComplexGet(3.0, 4.0);
		System.out.printf("Som = %.1f + %.1fi"+"\n", getal1.optellen(getal2).getReal(), getal1.optellen(getal2).getImaginair());
		System.out.printf("Vermenigvuldiging = %.1f + %.1fi"+"\n", (getal1.vermenigvuldigen(getal2)).getReal(), (getal1.vermenigvuldigen(getal2)).getImaginair());
		System.out.printf("Inverteren = %.1f + %.1fi", (getal1.inverteren()).getReal(), (getal1.inverteren()).getImaginair());
 
 
 
	}
 
}

public class ComplexGet {
	private double re, im;
 
	public ComplexGet(double re, double im) {
		this.re=re;
		this.im=im;
	}
 
	public ComplexGet() {
		this.re = 0;
		this.im = 0;
	}
 
	public double getReal() {
		return re;
	}
 
	public void setReal(double re) {
		this.re = re;
	}
 
	public double getImaginair() {
		return im;
	}
 
	public void setImaginair(double im) {
		this.im = im;
	}
 
	public ComplexGet optellen(ComplexGet x) {
		ComplexGet resultaat = new ComplexGet();
		resultaat.re = this.getReal() + x.getReal();
		resultaat.im = this.getImaginair() + x.getImaginair();
		return resultaat;
 
	}
 
	public ComplexGet vermenigvuldigen(ComplexGet x) {
		ComplexGet resultaat = new ComplexGet();
		resultaat.re = ((this.getReal() * x.getReal()) - (this.getImaginair() * x.getImaginair()));
		resultaat.im = ((this.getReal() * x.getImaginair()) + (this.getImaginair() * x.getReal()));
		return resultaat;
 
	}
 
	public ComplexGet inverteren() {
		ComplexGet resultaat = new ComplexGet();
		resultaat.re = ((this.getReal()) / (this.getReal() * this.getReal())+ (this.getImaginair() * this.getImaginair()));
		resultaat.im = ((this.getImaginair()) / (this.getReal() * this.getReal())+ (this.getImaginair() * this.getImaginair()));
		return resultaat;
	}

The "vermenigvuligen" en "optellen" are now correct the only this that is wrong is "inverteren". It means the invert of an complex number.

Som = 4,0 + 6,0i
Vermenigvuldiging = -5,0 + 10,0i
Inverteren = 5,0 + 6,0i

This is what the console gives. The right solution by "inverteren" should be 0,2 + -0.4i

**Norm** · February 25th, 2019, 12:50 PM

The conversion to an immutable (unchangeable) class is a good start.
The next step would be to make re and im final so that their values can not be changed after being set in the constructor.
Then in the optellen and vermenigvuldigen methods compute the re and im values and use them in the ComplexGet's constructor with the two arguments to create the instance to be returned.

Why does the inverteren method use the current object's values? The old version did not which meant that it could have been a static method.

**jim829** · February 25th, 2019, 01:14 PM

You need to verify your calculations in the inverteren method.

Regards,
Jim

**TmDee** · February 26th, 2019, 03:35 AM

Thanks Norm and Jim for the help! I found it let me show it.

This is the main:

public class main {
 
	public static void main(String[] args) {
		ComplexGet getal1 = new ComplexGet(1.0, 2.0);
		ComplexGet getal2 = new ComplexGet(3.0, 4.0);
		System.out.printf("Som = %.1f + %.1fi"+"\n", getal1.optellen(getal2).getReal(), getal1.optellen(getal2).getImaginair());
		System.out.printf("Vermenigvuldiging = %.1f + %.1fi"+"\n", (getal1.vermenigvuldigen(getal2)).getReal(), (getal1.vermenigvuldigen(getal2)).getImaginair());
		getal1.inverteren();
 
 
 
	}
 
}

And this is the Class ComplexGet:

public class ComplexGet {
	private double re, im;
 
	public ComplexGet(double re, double im) {
		this.re=re;
		this.im=im;
	}
 
	public ComplexGet() {
		this.re = 0;
		this.im = 0;
	}
 
	public double getReal() {
		return re;
	}
 
	public double getImaginair() {
		return im;
	}
 
	public ComplexGet optellen(ComplexGet x) {
		ComplexGet resultaat = new ComplexGet();
		resultaat.re = this.getReal() + x.getReal();
		resultaat.im = this.getImaginair() + x.getImaginair();
		return resultaat;
 
	}
 
	public ComplexGet vermenigvuldigen(ComplexGet x) {
		ComplexGet resultaat = new ComplexGet();
		resultaat.re = ((this.getReal() * x.getReal()) - (this.getImaginair() * x.getImaginair()));
		resultaat.im = ((this.getReal() * x.getImaginair()) + (this.getImaginair() * x.getReal()));
		return resultaat;
 
	}
 
	public void inverteren() {
		System.out.printf("Inverteren = %.1f + %.1fi", (this.getReal()) / (this.getReal() * this.getReal()+ this.getImaginair() * this.getImaginair()), (-this.getImaginair()) / (this.getReal() * this.getReal()+ this.getImaginair() * this.getImaginair()));
	}
 
}

And this is the console like it should be:

Som = 4,0 + 6,0i
Vermenigvuldiging = -5,0 + 10,0i
Inverteren = 0,2 + -0,4i

Thanks for the help again, appreciate it!

**Norm** · February 26th, 2019, 06:55 AM

The class is not correct yet. The variables: re and im need to be final so that their values can not be changed.

**TmDee** · February 26th, 2019, 10:59 AM

What do you mean final?

**Norm** · February 26th, 2019, 11:13 AM

final is a keyword that sets a variable's definition to say the variable's value can not be changed.

final int notToBeChanged = 123;

**jim829** · February 26th, 2019, 12:30 PM

But if you define it like this.

final int val;

It can be set initially, like in a constructor, but then can't change again. If you set the variables to private without outside access the users of your class can't change it. But making it final does protect you against accidentally changing the values yourself. Remember the 're' situation. It would have caught that. So it's a good idea to make your immutable variables final.

EDIT: One more thing about immutable classes. When using getters to get some field, if you are not returning primitives (int, double, etc) or other immutable objects (String, Integer, Double), you should return copies of the objects. For example, consider an array of items. Don't return the array reference because someone can change the internals and affect the original value. Return a copy of the array. With a collection, wrap it in an unmodifiable wrapper or make a copy to return.

Regards,
Jim

**TmDee** · February 27th, 2019, 08:25 AM

Okay I read this and kinda understand this, but I think my prof will teach us later about that thanks tho both for the help! Really appreciate it!!

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