Encapsualtion is used to make class members non-accesible outside the class.

We can make some class members private and the only way to assign values to them is by making an object of the class printer i.e we can only instantiate them using the constructors as these members are private members

And the only way to access these private members is by using getters and setters. We can never access them using objects of Printer class like -----------printerObject.tonerLevel as these members are private.

So basically encapsulation is all about setting members private and only accessing them using proper getter methods in other classes.

Benefits of encapsulation

1. Class variables can be made private and can be only accessed using setters and getters.

2.We can apply validations i.e set value of pagesPrinted = 2 only if pagesPrinted >0 etc

3.Since variables go through validations and can be only set if they pass certain validations so invalid values can't be assigned like pagesPrinted = -2 etc

Example

    private int tonerLevel;
    private int pagesPrinted;
    private boolean duplexPrinter;
   
//setting class member values in contructor
    public Printer(int tonerLevel, boolean duplexPrinter) {
        if(tonerLevel >=1 && tonerLevel<=100){
            this.tonerLevel = tonerLevel;
        }
        else
        this.tonerLevel = -1;
        this.duplexPrinter = duplexPrinter;
    }
 
//setting values using helper method
    public int addToner(int tonerAmount){
        if(tonerAmount>0 && tonerAmount <100) {
            if(this.tonerLevel +tonerAmount >100)
            return -1;
            this.tonerLevel += tonerAmount;
            return this.tonerLevel;
        }
        else{
            return -1;
        }
    }
 //getters for class members
    public int getTonerLevel() {
        return tonerLevel;
    }

    public int getPagesPrinted() {
        return pagesPrinted;
    }

//setters for class members
    public void setTonerLevel(int tonerLevel) {
        this.tonerLevel = tonerLevel;
    }
  //another helper method
    public int printPages(int pages){
        int pagesToPrint = pages;
        if(this.duplexPrinter){
            pagesToPrint = pages/2 +pages%2;
            System.out.println("Printing in duplex mode");
        }
        this.pagesPrinted +=pagesToPrint;
        return pagesToPrint;
    }
}