[SOLVED] AreaOfRectangle, compile-time error...Solution

1) Write a static method called AreaOfRectangle that is passed two float-point values for the length and width of a rectangle. The method returns the product of the length and width as a double. Comment the method using javadoc conventions. Write a main method that creates the following variables to describe the sides of a rectangle:double length = 3.4;
double width = 8.4;The main method should print the length, width, and area of the rectangle.

2) Why does the following code contain a compile-time error?public class Area
{
public static void main(String[] args)
{
int x = 2;
int y = 3;
System.out.println(“x: ” + x + ” y: ” + y + ” Sum: ” + sum(x,y));
}
/**
Computes the sum of two arguments.
@param a an int operand to be added
@param b another int operand
@return the sum of a and b
*/
public static int sum(int a, int b)
{
return a + b;
System.out.println(“Finished adding…”);
}
}3) Run the following code. The sum method in this program violates a design principle of the book (that methods should not try to modify an argument) when it assigns 5 to a, and 6 to b. Certainly these values are changed; this can be seen by examining the value the sum method returns. But what about arguments x and y? Are their values changed, too? In other words: Do the assignments made in the method body have side effects in the main program?
public class Area
{
public static void main(String[] args)
{
int x = 2;
int y = 3;
System.out.println(“x: ” + x + ” y: ” + y + ” Sum: ” + sum(x, y));
}
/**
Computes the sum of two arguments.
@param a an int operand to be added
@param b another int operand
@return the sum of a and b
*/
public static int sum(int a, int b)
{
a = 5;
b = 6;
return a + b;
}
}4.1) Write a method called makeRow that is passed two arguments: an int n and a String s, and which returns a String containing n copies of s, concatenated in a row. For instance, if we call the method with makeRow(5, “*”), the method returns *****. Write a main method that uses the method to print the string *****=====*****.

4.2) Reuse makeRow to write a method called printUpTriangle that is passed two arguments, an int n and a String s. It should print a right triangle in which the base of the triangle is made of n copies of s, and the vertex of the triangle has a single copy of s on the right. For example, calling printUpTriangle(13, “*”); prints the following lines:*
**
***
****
*****
******
*******
********
*********
**********
***********
************
*************Write a main method that calls printUpTriangle(13, “*”).

4.3) Reuse makeRow by writing a method called printDownTriangle that is passed an int n and a String s, and that prints a right triangle in which the base (at the top) of the triangle is made of n copies of s, and the vertex of the triangle has a single copy of s on the right. For example, calling printDownTriangle(13, “*”); prints the following lines:*************
************
***********
**********
*********
********
*******
******
*****
****
***
**
*Write a main method that calls printDownTriangle(13, “*”).