Multiple interface implementation in PHP - Step-by-Step Execution

Concept Flow - Multiple interface implementation

Define Interface A

↓

Define Interface B

↓

Create Class implementing A and B

↓

Implement all methods from A and B

↓

Create object of Class

↓

Call methods from both interfaces

The class promises to follow rules from both interfaces by implementing all their methods.

Execution Sample

PHP

<?php
interface A {
  public function foo();
}
interface B {
  public function bar();
}
class MyClass implements A, B {
  public function foo() { return "foo called"; }
  public function bar() { return "bar called"; }
}
$obj = new MyClass();
echo $obj->foo();
echo $obj->bar();
?>

This code shows a class implementing two interfaces and calling their methods.

Execution Table

Step	Action	Evaluation	Result
1	Define interface A with method foo()	Interface A created	Interface A ready
2	Define interface B with method bar()	Interface B created	Interface B ready
3	Create class MyClass implementing A and B	Class MyClass created	Class ready with interfaces A and B
4	Implement method foo() in MyClass	Method foo() defined	foo() returns 'foo called'
5	Implement method bar() in MyClass	Method bar() defined	bar() returns 'bar called'
6	Create object obj of MyClass	Object created	obj is instance of MyClass
7	Call obj->foo()	Calls foo()	Output: 'foo called'
8	Call obj->bar()	Calls bar()	Output: 'bar called'
9	End of script	No more code	Execution stops

💡 All interface methods implemented; object methods called; script ends

Variable Tracker

Variable	Start	After Step 6	After Step 7	After Step 8	Final
obj	undefined	instance of MyClass	instance of MyClass	instance of MyClass	instance of MyClass

Key Moments - 2 Insights

Why must MyClass implement all methods from both interfaces A and B?

Because PHP requires that a class implementing interfaces must define all their methods, as shown in steps 4 and 5 of the execution_table.

What happens if MyClass misses implementing one method from an interface?

PHP will give an error and stop execution, because the class does not fulfill the interface contract, which is why steps 4 and 5 are important.

Visual Quiz - 3 Questions

Look at the execution_table, what is the output after calling obj->foo() at step 7?

A No output

B "bar called"

C "foo called"

D Error

💡 Hint

Check the 'Result' column at step 7 in the execution_table

At which step does the object obj get created?

A Step 6

B Step 4

C Step 7

D Step 3

💡 Hint

Look for 'Create object obj' in the 'Action' column of execution_table

If MyClass did not implement method bar(), what would happen?

A The script runs normally

B PHP throws an error at class creation

C Only foo() works, bar() is ignored

D The object cannot be created

💡 Hint

Refer to key_moments about missing method implementation consequences

Concept Snapshot

Multiple interface implementation in PHP:
- Use 'implements' keyword with comma-separated interfaces.
- Class must define all methods from all interfaces.
- Allows one class to follow multiple contracts.
- Example: class MyClass implements A, B { ... }
- Missing methods cause errors.

Full Transcript

This example shows how a PHP class can implement multiple interfaces by listing them after the 'implements' keyword. Each interface defines methods that the class must provide. The class MyClass implements interfaces A and B, so it defines both foo() and bar() methods. An object of MyClass is created and both methods are called, producing outputs 'foo called' and 'bar called'. If any method from the interfaces is missing, PHP will throw an error. This ensures the class follows all interface rules.