● for loop vs. while loop
o for loops repeat for a range of values
o while loops repeat when a condition is true/met
o for loops have a start value for the loop variables
o for loop can be best when you know how many times to repeat the code
o while loops can be best when you don’t know how many times to repeat the code
● Similarities between for loops and while loops
o Repeats code
o Loop stops once the condition is false
● Example of a while loop
public class Test
{
public static void main(String[] args)
{
int x = 10;
while (x > 0)
{
System.out.println(x);
x = x - 2;
}
}
}
● Example of a for loop
public class Test
{
public static void main(String[] args)
{
for (int x = 3; x > 0; x--)
{
System.out.println(x);
}
}
}
● Body of the loops
o A single statement after “while” or “for”
OR
o Block of code between the opening and closing curly braces.
● Loops are usually incorporated in:
o String traversals
o String processing
o The code processes a string by each character.
● First character in a Java String ALWAYS starts with the index 0
o Last character: length() – 1
● String methods that are often used:
o int length()
o int indexOf(String Str)
o String substring (int from, int to)
o String substring (int from)
● Standard algorithms use String traversals to:
o Find if the substrings have a certain property
o Determine how many substrings meet the criteria
o Create new strings with the characters of an existing string reversed.
● Nested loops – a loop inside of another loop
● Used when working with two dimensions such as arrays and ArrayLists.
● The inner loop runs multiple times before the outer loop runs again.
● Inner loop must finish all iterations before the outer loop can go onto the next iteration.
● Example of a nested loop:
public class NestedLoops
{
public static void main(String[] args)
{
for (int row = 1; row <= 3; row++)
{
for (int col = 1; col <= 5; col++)
{
System.out.print("*");
}
System.out.println();
}
}
}
● Trace tables – used to keep track of the variables
o Keeps track of any values assigned in each iteration of the loop
● Statement Execution Count – determines how many times a block of code runs
o Known as run-time analysis
● largestValue – smallestValue + 1
o Number of times a loop executes