Complex Objects

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Here a complex object case.

We have three types of objects:
String, Coor1D, and Point1D.

... 
"A"
... 
"B"
...

First, we handle String literals.

String strA;

causes two actions:

allocates a location in the symbol table for strA of type String.
allocates a location in the memory to store reference to String.

strA = "A";

connects strA to literal "A"

Coor1D c1;

causes two actions:

allocates a location in the symbol table for c1 of type Coor1D.
allocates a location in the memory to store reference to Coor1D.

It is exactly the same as what
String strA; does.

c1 = new Coor1D(1);

causes two actions:

creates a new object of type Coor1D.
- Coor1D has one field x.
  - We need one memory location of type int.
This is the constructor of Coor1D:
```
public class Coor1D {

	int x;

	public Coor1D(int x) {
		this.x = x;
	}
	...
}
```

c1 = new Coor1D(1);

causes two actions:

creates a new object of type Coor1D.
- Coor1D has one field x.
  - We need one memory location of type int.
This is the constructor of Coor1D:
```
public class Coor1D {

	int x;

	public Coor1D(int x) {
		this.x = x;
	}
	...
}
```
connects c1 to the new object.

Point1D p1;

as String strA; or Coor1D c1, causes two actions:

allocates a location in the symbol table for p1 of type Point1D.
allocates a location in the memory to store reference to Point1D.

p1 = new Point1D(strA, c1);

is the most complex statement of this visualization because of Point1D itself is a complex object.

public class Point1D {

	String name;
	Coor1D coordinate;
	...
}

It has two fields name and coordinate
- both are objects
Since
- strA is of type String, and
- c1 is of type Coor1D,
this is a call to constructor
- with the signature Point1D(String, Coor1D).

The first constructor of Point1D is called:

public class Point1D {

	String name;
	Coor1D coordinate;

	public Point1D(String name, Coor1D c) {
		this.name = name;
		this.coordinate = c;
	}
	
	public Point1D(String name, int x) {
		...
	}
	...
}

p1 = new Point1D(strA, c1);

causes a number of actions

allocates two memory locations for new Point1D object

public class Point1D {

	String name;
	Coor1D coordinate;

	...
}

p1 = new Point1D(strA, c1);

causes a number of actions

allocates two memory locations for new Point1D object

one location refers to where strA refers

public class Point1D {

	String name;
	Coor1D coordinate;

	public Point1D(String name, Coor1D c) {
		this.name = name;
		...
	}
	...
}

p1 = new Point1D(strA, c1);

causes a number of actions

allocates two memory locations for new Point1D object
one location refers to where strA refers

the other location refers to where c1 refers

public class Point1D {

	String name;
	Coor1D coordinate;

	public Point1D(String name, Coor1D c) {
		...
		this.coordinate = c;
	}
	...
}

p1 = new Point1D(strA, c1);

causes a number of actions

allocates two memory locations for new Point1D object
one location refers to where strA refers
the other location refers to where c1 refers
Since the object is created, we can connects p1 to the new object

Point1D p2;

does as expected

allocates a location in the symbol table for p2 of type Point1D.
allocates a location in the memory to store reference to Point1D.

It is no different then Point1D p1;, String strA; or Coor1D c1.

p2 = new Point1D("B", 7);

This is the second most complex statement of this visualization.

It is different then

p1 = new Point1D(strA, c1);

Since
- "B" is of type String, and
- 7 is of type int,
this is a call to another constructor
- The signature is Point1D(String, int).

The second constructor of Point1D is called:

public class Point1D {

	String name;
	Coor1D coordinate;
	
	public Point1D(String name, Coor1D c) {
		...
	}
	
	public Point1D(String name, int x) {
		this.name = name;
		this.coordinate = new Coor1D(x);
	}
	...
}

Note that within the constructor, there is a new
- new Coor1D(x)

p2 = new Point1D("B", 7);

causes a number of actions

allocates two memory locations for new Point1D object

public class Point1D {

	String name;
	Coor1D coordinate;

	...
}

p2 = new Point1D("B", 7);

causes a number of actions

allocates two memory locations for new Point1D object

one location refers to where literal "B" resides.

public class Point1D {

	String name;
	Coor1D coordinate;
	
	public Point1D(String name, Coor1D c) {
		...
	}
	
	public Point1D(String name, int x) {
		this.name = name;
		...
	}
	...
}

p2 = new Point1D("B", 7);

causes a number of actions

allocates two memory locations for new Point1D object
one location refers to where literal "B" resides.

the other location should refer to a Coor1D object but we have 7.

Constructor tells us how to obtain a Coor1D object from 7

public class Point1D {

	String name;
	Coor1D coordinate;
	...
	public Point1D(String name, int x) {
		this.name = name;
		this.coordinate = new Coor1D(x);
	}
	...
}

So let's construct it using
```
new Coor1D(7);
```
similar to
```
c1 = new Coor1D(1);
```

p2 = new Point1D("B", 7);

causes a number of actions

allocates two memory locations for new Point1D object
one location refers to where literal "B" resides.

the other location should refer to a Coor1D object.

Constructor tells us how to obtain a Coor1D object from 7

public class Point1D {

	String name;
	Coor1D coordinate;
	...
	public Point1D(String name, int x) {
		this.name = name;
		this.coordinate = new Coor1D(x);
	}
	...
}

So, let's construct it using
```
new Coor1D(7);
```
similar to
```
c1 = new Coor1D(1);
```
Then connect the new object to this.coordinate

p2 = new Point1D("B", 7);

causes a number of actions

allocates two memory locations for new Point1D object
one location refers to where literal "B" resides.

the other location should refer to a Coor1D object.

Constructor tells us how to obtain a Coor1D object from 7

public class Point1D {

	String name;
	Coor1D coordinate;
	...
	public Point1D(String name, int x) {
		this.name = name;
		this.coordinate = new Coor1D(x);
	}
	...
}

So, let's construct it using
```
new Coor1D(7);
```
similar to
```
c1 = new Coor1D(1);
```
Then connect the new object to this.coordinate

Finally, connect p2 to newly created Point1D object.

Objects are not that easy, isn't it?

That's it.