Constructor overloading in Java - Step-by-Step Execution

Concept Flow - Constructor overloading

Create object

↓

Check constructor parameters

↓

Call default constructor

↓

Call constructor with int

↓

Call constructor with two args

↓

Initialize object fields

↓

Object ready to use

When creating an object, Java chooses the constructor matching the given parameters to initialize the object.

Execution Sample

Java

class Box {
  int width, height;
  Box() { width = 0; height = 0; }
  Box(int w) { width = w; height = w; }
  Box(int w, int h) { width = w; height = h; }
}

Defines a Box class with three constructors: no parameters, one int, and two ints.

Execution Table

Step	Constructor Called	Parameters	Field width	Field height	Action
1	Box()	none	0	0	Default constructor sets width and height to 0
2	Box(int w)	5	5	5	Single parameter constructor sets width and height to w
3	Box(int w, int h)	3, 7	3	7	Two parameter constructor sets width and height separately
4	End	-	-	-	All objects created with correct fields

💡 All constructors executed as per parameters; object initialization complete.

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
width	undefined	0	5	3	3
height	undefined	0	5	7	7

Key Moments - 3 Insights

Why does Java choose different constructors for the same class?

Java matches the constructor parameters with the arguments used during object creation, as shown in execution_table rows 1-3.

What happens if no constructor matches the parameters?

Java will give a compile-time error because it cannot find a suitable constructor, unlike the examples where parameters match exactly.

Are the fields initialized differently in each constructor?

Yes, each constructor sets the fields differently based on the parameters, as seen in the field values in execution_table rows 1-3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of height after step 2?

A 0

B 5

C 7

D undefined

💡 Hint

Check the 'Field height' column in execution_table row 2.

At which step does the constructor set width to 3?

A Step 1

B Step 2

C Step 3

D No step

💡 Hint

Look at the 'Field width' column in execution_table rows.

If we create a Box object with no parameters, which constructor is called?

A Box()

B Box(int w, int h)

C Box(int w)

D No constructor

💡 Hint

Refer to execution_table row 1 for constructor called with no parameters.

Concept Snapshot

Constructor overloading means having multiple constructors with different parameters.
Java picks the constructor matching the arguments when creating an object.
Each constructor can initialize fields differently.
If no matching constructor exists, code won't compile.
Use overloading to create flexible object initialization.

Full Transcript

Constructor overloading in Java allows a class to have multiple constructors with different parameter lists. When an object is created, Java chooses the constructor that matches the given arguments. For example, a Box class can have a default constructor with no parameters, one with a single integer parameter, and one with two integer parameters. Each constructor sets the object's fields differently. This lets you create objects in different ways. If you try to create an object with parameters that don't match any constructor, Java will give an error. The execution table shows step-by-step which constructor is called and how the fields change. This helps understand how overloading works in practice.