Lab 1 Manual [Lab Manual] CS 204 DSA Writing Generic Methods And Classes

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Spring 2019
CS-204: Data Structures and Algorithms
Lab-1 Manual
Writing Generic Methods and Classes
v1.0
3/23/2019
GIFT School of Engineering
and Applied Sciences
Lab-1 Manual
2019
Page 1
Task #1: Writing Methods in Java
In this task, you are being asked to write a method printArray which takes an Integer array as an
argument, and then prints the values of array on the console. You may use the following method
header:
public void printArray(Integer[] inputArray)
Now, create an overloaded method with the same name to print values from a Double array
argument. You may use the following method header:
public void printArray(Double[] inputArray)
Finally, create another overloaded method with the same name to print values from a String array.
You may use the following method header:
public void printArray(String[] inputArray)
1. Create a class with the name GenericsLab1.java.
2. Create appropriate arrays: intArray, doubleArray, stringArray of types Integer, Double
and String.
3. Insert values in all arrays. Do not use a Scanner for any inputs.
4. Make appropriate method calls for above created arrays and print the values.
5. Give appropriate message while printing values.
Lab-1 Manual
2019
Page 2
What are Generic Methods?
You can write a single generic method declaration that can be called with arguments of different
types. Based on the types of the arguments passed to the generic method, the compiler handles
each method call appropriately. Following are the rules to define Generic Methods:
1. All generic method declarations have a type parameter section delimited by angle brackets
(< and >) that precedes the method's return type ( < T > in the coming example).
2. Each type parameter section contains one or more type parameters separated by commas.
A type parameter, also known as a type variable, is an identifier that specifies a generic
type name.
3. The type parameters can be used to declare the return type and act as placeholders for the
types of the arguments passed to the generic method, which are known as actual type
arguments.
4. A generic method's body is declared like that of any other method. Note that type
parameters can represent only reference types, not primitive types (like int, double and
char).
5. Below is an example of a generic method, which takes a generic argument of type T and
prints its value regardless of its type:
public <T> void printGenericValue(T var) {
System.out.println(var);
}//printGenericValue
Task #2: Writing a Generic Method in Java
In this task, you are being asked to write a generic method printArray which takes a generic array
as an argument, and then prints the values of array on the console without specifying the type for
the array. You may use the following method header:
public <T> void printArray(T[] inputArray )
1. Create a program called GenericMethodsLab1.java
2. Create the method printArray with the generic data type.
3. Create appropriate arrays: intArray, doubleArray, stringArray of types Integer, Double
and String having appropriate values.
4. Create an appropriate call for the generic method you created above for all arrays intArray,
doubleArray, and stringArray and print the values.
5. Give appropriate messages while printing values.
Lab-1 Manual
2019
Page 3
What are Bounded Type Parameters?
There may be times when you'll want to restrict the kinds of types that can be passed to a type
parameter. For example, a method that operates on numbers might only want to accept instances
of Number or its subclasses. This is what bounded type parameters are for.
To declare a bounded type parameter, list the type parameter's name, followed by the extends
keyword, followed by its upper bound.
Example
Following example illustrates how extends is used in a general sense to mean either "extends" (as
in classes) or "implements" (as in interfaces). This is an example which takes two generic
arguments and return true if the numbers are equal, otherwise returns false.
public <T extends Number> boolean isEqual(T number1, T number2)
{
if (number1.doubleValue() != number2.doubleValue()) {
return false;
} else {
return true;
}//if
}//isEqual
Task #3: Writing a Generic Method with Bounded Type Parameters
In this task, you are being asked to write a generic method largestValue that takes three generic
arguments and prints the largest value from the given arguments. The arguments must be bounded
to Numbers only, that means that the method will not accept any other type, such as String values
except number values. The numbers could be of types Float, Double or Integer. You may use the
following method header:
public <T extends Number> void largestValue(T number1,
T number2, T number3)
1. Create a program called BoundedTypeLab1.java
2. Create the method largestValue with three generic data types.
3. Create 3 variables of type Double having appropriate values and call the largestValue
method.
4. Create 3 variables of type Integer having appropriate values and call the largestValue
method.
Lab-1 Manual
2019
Page 4
What are Generic Classes?
A generic class declaration looks like a non-generic class declaration, except that the class name
is followed by a type parameter section. As with generic methods, the type parameter section of a
generic class can have one or more type parameters separated by commas. These classes are known
as parameterized classes or parameterized types because they accept one or more parameters.
Example
public class Box<T> {
private T value;
public void setValue(T value) {
this.value = value;
}//Setter
public T getValue() {
return this.value;
}//Getter
public static void main(String[] args) {
//Creating Objects with the Generic Class
Box<Integer> integerBox = new Box<Integer>();
Box<String> stringBox = new Box<String>();
//Setter Calling for setting values in the Generic
//variable value
integerBox.setValue(new Integer(10));
stringBox.setValue(new String("Hello World"));
//Printing Values
System.out.println("Integer Value: " +
integerBox.getValue());
System.out.println("String Value: " +
stringBox.getValue());
}//main
}//class
NOTE: Open the Box.java code from the Code folder. Compile and run the code.
Lab-1 Manual
2019
Page 5
Task #4: Writing a Generic Class
In this task you are being asked to write a simple generic class GenericClass<T> which has two
generic private data members, and you are asked to implement its constructor, setter and getter
methods, and the print method which will print the state of the object with appropriate messages.
You may use the following skeleton code that has been placed in the Code folder:
public class GenericClassLab1<T> {
private T obj1;
private T obj2;
//Constructor
public GenericClassLab1(T obj1, T obj2) {
}//GenericClass
//Setters
public void setObj1(T obj1) {
}//Set Obj1
public void setObj2(T obj2) {
}//Set Obj2
//Getters
public T getObj1() {
}//get Obj1
public T getObj2() {
}//get Obj2
//print the state
public void print() {
}//print
}//class
1. Open the file GenericClassLab1.java from the Code folder.
2. Complete the implementation of the constructor, setter and getter methods, and the print
method.
3. Create a test program called TestGenericClassLab1.java having the main method.
4. Create an object of GenericClassLab1 with the Integer data type and print values.
5. Next, create an object of GenericClassLab1 with the Double data type and print values.
6. Finally, create an object of GenericClassLab1 with the String data type and print values.

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