Lecture 14, CS 302-7 and 8, February 22

1. Reminders
1. Program 1

i. Due Friday night

ii. Input validation - .hasNextInt, .next

iii. Reminder – documentation

iv. Reminder – don’t try to do ‘too much’

2. Review
1. Arrays

i. Declare/initialize

1. int[] numbers=new int[3];

2. int[] numbers; numbers=new int[3];

3. int[] numbers={1,2,3};

ii. Use

1. numbers[1] (‘numbers sub 1’) -> 2

2. numbers[0] -> 1

iii. Characteristics

1. Type – int, double, String, etc

2. Length - numbers.length

3. More about arrays as references
1. If we set two array variables equal to the same array, then updating one updates the other
2. Example – RefArray.java
4. For each loop
1. Structure

i. int[] data = {…};

For( int value : data)

{

// body

}

2. Example – TestScores.java
4. Things you can do with Arrays
1. Many of the same things we did with loops – sums, averages, Max, min. etc – except, now we remember data

i. Note –these require traversing the entire array

2. Linear search

i. Start at beginning, search until we find data

ii. Note – search can abort early, once we find answer

3. Binary Search

i. Faster than linear

ii. Condition – array is sorted

iii. Real-world example – searching through a dictionary.

1. Start in middle, then half each way, etc.

4. Inserting and removing elements

i. Remove – start at one above, copy down

ii. Insert – start from end, copy up, then put item in

1. Harder than remove

5. Copying

i. Int[] numbers2=Arrays.copyOf(numbers, numbers.length);

6. Methods
1. Think about our Java programs so far – we’ve put everything in this section called main

i. Public static void main(String[] args)

2. What is a method? A method is a block of code that performs some task.
3. We’ll now write our own additional static methods
4. Why?

i. Modularity

ii. Maintainability/readability

iii. Reduce redundancy

5. Think of methods as black boxes
6. Examples that we’ve seen already:

i. Math.pow, Arrays.copyOf

7. Methods have inputs and outputs:

i. Inputs – parameters/arguments or parameter variables/parameter values

1. can be multiple

2. declare in method header

ii. Outputs – return values

1. only one

2. specify with return statement

3. declare in method header

iii. example - Math.pow(2,3) //2^3

8. Syntax

i. Declaring :

public static <return type> <name>(<paramVars>) {

//body

//return <returnVal>;

}

ii. Calling:

<ClassName>.<methodName>(<paramVals>); //Returns <returnVal>

7. HW
1. Read 5.1-5.2