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Learning the Java Language
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Classes and Objects
Questions and Exercises: Objects
Questions
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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());
}
}
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The following code creates one
Point
object
and one
Rectangle
object.
How many references to those objects exist after the code executes?
Is either object eligible for garbage collection?
...
Point point = new Point(2,4);
Rectangle rectangle = new Rectangle(point, 20, 20);
point = null;
...
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How does a program destroy an object that it creates?
Exercises
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Fix the program called
SomethingIsWrong
shown in Question 1.
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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.