In TypeScript, all members in a class are public by default. We have to add the private keyword explicitly to control the visibility of the members:

class SimpleCalculator { 
    private x: number; 
    private y: number; 
    z: number; 
    constructor(x: number, y: number) { 
       this.x = x; 
       this.y = y; 
    } 
    addition() { 
        z = x + y; 
    } 
    subtraction() { 
        z = x - y; 
    } 
} 
class ComplexCalculator { 
    z: number; 
    constructor(private x: number, private y: number) { } 
    multiplication() { 
        z = this.x * this.y; 
    } 
    division() { 
        z = this.x / this.y; 
    } 
} 

Note that in the SimpleCalculator class, we defined x and y as private properties, which will not be visible outside the class. In ComplexCalculator, we defined x and y using parameter properties. These parameter properties will enable us to create and initialize the member in one statement. Here, x and y are created and initialized in the constructor itself without writing any further statements inside it. Also, x and y are private in order to hide them from exposure to consuming classes or modules.