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1. Java, Arrays, and Sorting¶

Douglas Blank, Fall 2015, CS110: Introduction to Computing

Table of Contents¶

1. Java, Arrays, and Sorting

1.1 Review¶

We can now:

define new types using the class keyword
create new instances of a type with the new keyword
call methods of instance by using the dot

This whole philosophy is called Object Oriented Programming or OOP. Type and object are largely synonyms.

Objects are typically nouns
Methods (ie, functions in classes) are verbs
Properties values are adjectives
this is a pronoun that means me

1.1.1 An example:¶

Imagine the alien creature Zoog from http://www.openprocessing.org/sketch/12199:

class Zoog {
    Zoog(float tempX, float tempY, float tempW, 
         float tempH, float tempEyeSize, 
         float tempBodyColor1, float tempBodyColor2, float tempBodyColor3) {
        // ...
    }
    void jiggle(float speed) {
        // ...
    }
    void display(color eyeColor) {
        // ...
    }
}

Created file '/home/dblank/public_html/CS110 Intro to Computing/2015-Fall/Lectures/Zoog.java'.

%include Zoog.java

// x, y, width, height, eye size, r, g, b:
Zoog zoog1 = new Zoog(20, 70, 30, 10, 5, 128, 0, 0);
Zoog zoog2 = new Zoog(50, 70, 30, 20, 5, 0, 128, 0);
Zoog zoog3 = new Zoog(80, 70, 30, 30, 5, 0, 0, 128);

void setup() {
    // eye color:
    zoog1.display(color(128, 0, 0));
    zoog2.display(color(255, 0, 0));
    zoog3.display(color(128, 0, 0));
}

1.2 Java¶

The truth about Java:

All code must be in a class, in a file
Code must be "compiled"
There is a special method called main whose type is public static void
- public, because it can be seen from outside the class
- static, because it doesn't require an "instance"
- void, as before, it doesn't return anything

In Jupyter, we can create a file in a number of ways. The easiest is to use the %%file magic:

%%file SomeClass.java

public class SomeClass {

    public static void main(String[] args) {
        System.out.println("Hello, world!");
    }
}

Created file '/home/dblank/public_html/CS110 Intro to Computing/2015-Fall/Lectures/SomeClass.java'.

Then we compile the file using the Java Compiler, javac:

%%shell
    
javac SomeClass.java

Finall, we can run the file using the Java Runtime called java:

%%shell

java SomeClass

Hello, world!

1.2.1 Differences between Java and Processing?¶

1.3 Arrays¶

We saw that Java has arrays:

We can:

define an array with Type[] name
create space for the array with new Type[SIZE]
create individual items with new Type(...)

Zoog[] army;

army = new Zoog[1000];

for (int i; i < army.length; i++)  {
    army[i] = new Zoog(...);
}

1.3.1 Primitive types¶

int
float
bool

With primitive types, you don't have to do the third step:

int[] heights;

heights = new int[100];

1.3.2 Arrays and Functions¶

int biggest(int[] myarray) {
    // what goes here?
    int biggest_so_far = -10000;
    for (int i = 0; i < myarray.length; i++) {
        if (myarray[i] > biggest_so_far) {
            biggest_so_far = myarray[i];
        }
    }
    return biggest_so_far;
}

int smallest(int[] myarray) {
    // what goes here?
    int smallest_so_far = 10000;
    for (int i = 0; i < myarray.length; i++) {
        if (myarray[i] < smallest_so_far) {
            smallest_so_far = myarray[i];
        }
    }
    return smallest_so_far;
}

void printArray(int[] myarray) {
    print("[");
    for (int i = 0; i < myarray.length; i++) {
        print(myarray[i]);
        print(", ");
    }
    println("]");
}

int[] heights = new int[100];

void setup() {
    for (int i = 0; i < 100; i++) {
        heights[i] = int(random(50));
    }

    int b = biggest(heights);
    int s = smallest(heights);
    
    printArray(heights);

    println("Biggest: " + b + " Smallest: " + s);
}

1.4 Sorting¶

void sorted(int[] myarray) {
    // what goes here?
    for (int i = 0; i < myarray.length - 1; i++) {
        for (int j = i + 1; j < myarray.length; j++) {
            if (myarray[i] > myarray[j]) {
                int temp = myarray[i];
                myarray[i] = myarray[j];
                myarray[j] = temp;
                
            }
        }        
    }
}

void printArray(int[] myarray) {
    print("[");
    for (int i = 0; i < myarray.length; i++) {
        print(myarray[i]);
        print(", ");
    }
    println("]");
}

int[] heights = new int[100];

void setup() {
    for (int i = 0; i < 100; i++) {
        heights[i] = int(random(50));
    }
    
    printArray(heights);
    sorted(heights);
    printArray(heights);
}

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