how does this work?

Person person = new Person(); System.out.println("Age: " + person.age); person.adjustAge(person.age); System.out.println("Adjusted age: " + person.age); } public static class Person { public int age = 20; public void adjustAge(int age) { this.age = age + 20;

I meant ("AGE' "+ PERSON.AGE); // equal 20, but ("ADJUSTED AGE: "+ PERSON.AGE); equal 40

System.out.println method takes String as input and prints it to the console. This particular line:

System.out.println("Adjusted age: " + person.age);

Or this one:

System.out.println("Age: " + person.age);

Means following: String value "Adjusted age:" is concatenated with the actual value of the property person.age The result should be "Adjusted age: 40" Same for the first one - "Age: 20" You may read about String concatenation to get a better understanding of this. So basically what your code is doing is:

Person person = new Person();
System.out.println("Age: " + person.age);
person.adjustAge(person.age);
System.out.println("Adjusted age: " + person.age);

- Creating a new Person that has a predefined value in age property; - Printing this value to the console; - Calling to the person's object method adjustAge() that receives int value as argument and is setting a new value to the object's property age (in this particular case it is argument's value + 20). Since this method is called with an actual age value - you receive 20+20 in the end. You can play around with it by replacing this:

person.adjustAge(person.age);

With something like this:

person.adjustAge(123);

After all these steps you are just printing new age value to the console.