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The Java™ Tutorials
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Classes and Objects
Classes
Declaring Classes
Declaring Member Variables
Defining Methods
Providing Constructors for Your Classes
Passing Information to a Method or a Constructor
Objects
Creating Objects
Using Objects
More on Classes
Returning a Value from a Method
Using the this Keyword
Controlling Access to Members of a Class
Understanding Class Members
Initializing Fields
Summary of Creating and Using Classes and Objects
Questions and Exercises
Questions and Exercises
Nested Classes
Inner Class Example
Local Classes
Anonymous Classes
Lambda Expressions
Method References
When to Use Nested Classes, Local Classes, Anonymous Classes, and Lambda Expressions
Questions and Exercises
Enum Types
Questions and Exercises
Trail: Learning the Java Language
Lesson: Classes and Objects
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# Questions and Exercises: Objects

## Questions

1. What's wrong with the following program?

       public class SomethingIsWrong {
           public static void main(String[] args) {
               Rectangle myRect;
               myRect.width = 40;
               myRect.height = 50;
               System.out.println("myRect's area is " + myRect.area());
           }
       }

2. The following code creates one array and one string object. How many references to those objects exist after the code executes? Is either object eligible for garbage collection?

       ...
       String[] students = new String[10];
       String studentName = "Peter Parker";
       students[0] = studentName;
       studentName = null;
       ...

3. How does a program destroy an object that it creates?

## Exercises

1. Fix the program called `SomethingIsWrong` shown in Question 1.

2. Given the following class, called `NumberHolder`, write some code that creates an instance of the class, initializes its two member variables, and then displays the value of each member variable.

       public class NumberHolder {
           public int anInt;
           public float aFloat;
       }

Check your answers.

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