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#For Baihan Lin's daily practice

05/01/2016

###Review Plan

  1. Java
  • Basic Syntax
  • Key algorithms
  • Interface
  • GUI

  1. Algorithms

  2. Data Structure

  3. Mathematics

  4. Neural Network

  5. Data Mining

  6. Cellular Automata

  7. BGI

  8. Matlab

  9. Perl

  • Regularization
  1. R
  • PCA

  1. C ??

  2. Microsoft

  3. IEE

  4. Google

05/03/2016

###Java Basic Syntax

part i: very basic

public class name {
public static void main(string[] args) {
statement;
}
}

System.out.print("text");
System.out.println("text");

writing a static method is like adding a new command to Java

public static void name() {
statement
}

name();

Java's primitive types

  • int
  • double
  • char
  • boolean

integer vs. real number

  • integer division: 45 / 10 = 4
  • integer remainder: 45 % 10 = 5

String concatenation:

  • "hello" + 42 - 3*2 = "hello36"

Type casting

  • double result = (double) 19/5; // 3.8

increment

  • int++; double--;
  • x += 3; // x = x +3
  • x *= 2; // x = x * 2

for(initialization; test; update) {
statement;
}

Variable scope

Class constants

  • public static final int DAYS = 7;

Math Class

  • Math.abs(x)
  • Math.round(x)
  • Math.ceil(x)
  • Math.floor(x)
  • Math.log10(x)
  • Math.max(x, y) // Math.min(x, y)
  • Math.pow(base, exp)
  • Math.sqrt(x)
  • Math.sin(x) // cos, tan
  • Math.toDegrees(x) // toRadians
  • Math.random // 0 to 1
  • Math.E // Math.PI

public static double slope(int x, int y...) {
statement;
return ....;
}

Strings

  • indexOf(str) // -1 if not there
  • .length()
  • substring(inclusive, exclusive); // index2 optional
  • .toLowerCase() // .toUpperCase()
  • equals(str)
  • equalsIgnoreCase(str)
  • startsWith(str)
  • endsWith(str)
  • contains(str)
  • charAt(index)

char

  • 'P' vs. "P"

printf

  • System.out.printf("(%d, %d)\n", x, y) // (3, 2)
  • System.out.printf("%4d %4.2f\n", x, y) // 3 2.00

DrawingPanel (canvas)

  • DrawingPanel name = new DrawingPanel(width, height)

Graphics

  • Graphics g = panel.getGraphics();
  • g.drawLine(x1, y1, x2, y2)
  • g.drawRect(x, y, w, h)
  • g.fillRec(x, y, w, h) // g.fillOval(x, y, w, h)
  • g.drawString(txt, x, y)
  • g.setColor(Color)

Color

  • Color name = new Color(r, g, b)
  • constants (BLACK, BLUE, CYAN, GREEN...)

Scanner

  • System.out // for print and println
  • System.in // for Scanner
  • Scanner name = new Scanner(System.in)
  • Scanner console = new Scanner(System.in)
  • nextint()
  • nextDouble()
  • next() // String
  • nextLine() // String
  • hasNext() // hasNextint(), hasNextDouble(), hasNextLine()

if (test) {
statement;
} else {
statement;
}

test

  • ==, !=, <, >, >=, <=
  • &&, ||, !
  • boolean minor = (age < 21);

loop-and-a-half

while (test) {
statement;
}

do {
statement;
} while (test)

Random Class

  • Random rand = new Random();
  • int randomNumber = rand.nextInt(10);
  • nextInt(), nextDouble()

break

  • exit a loop

reading files

  • File file = new File("mydata.txt");
  • Scanner input = new Scanner(file)
  • Scanner input = new Scanner(new File("mydata.txt"));

throws

  • public static type name(params) throws type { statement;}

output to files

  • java.io
  • PrintSteam out1 = System.out;
  • PrintStream out2 = new PrintStream(new File("x.txt"));
  • out2.println("hello");

Arrays

  • index: 0-based
  • int[] numbers = new int[10]; // 0-9
  • numbers[0] = 27;
  • numbers.length
  • type[] name = {value, value, ...};
  • equals(array1, array2)
  • fill(array, value) // set every element in the array to be given value
  • sort(array) // sort into ascending order
  • toString(array) // "[10, 30, 7]"
  • binarySearch(array, value) // return index of given value in sorted (< 0 if not found)

Value vs. Reference semantics

  • int[] a1 = {1, 2, 3}; int[] a2 = a1; // affect both

classes and objects

fields

  • public class student {
    private String name;
    private double gpa;
    }

instance method (vs. static)

  • only exists inside each object of a class
  • public void shout() {}

Point class

  • in Graphics

implicit parameter

  • p1.draw(g) // p1

kinds of methods

  • accessor // examine object state
  • mutator // modify an object's state

constructors

  • run when use "new"
  • public type(params) {
    statements;
    }
  • public Point(int initialX, int initialY) {
    x = initialX;
    y = initialY;
    }

toString

  • every class has one

this

  • reference to implicit parameter
  • this.fields // refer to a field
  • this.method(params) // call a method
  • this(params) // call a constructor from another

static methods

  • part of a class, not part of an object
  • shared by all objects of that class
  • cannot use "this"
  • if public, can be called outside

inheritance

  • superclass vs. subclass
  • public class Secretary extends Employee {}
  • can override superclass's versions
  • super.method() // can call overrider methods with super

polymorphism

  • can only use superclass if used like below:
  • Employee ed = new LegalSecretary();
  • can only call Employee, but not LegalSecretary

05/07/2016

###Java Basic Syntax

part ii: medium

List

  • [], [apple, ABC, hello]
  • import java.util.*;

ArrayList

  • ArrayList name = new ArrayList()
  • .add(value)
  • .add(index, value)
  • .clear()
  • .indexOf(value)
  • .get(index)
  • .remove(index)
  • .set(index, value)
  • .size()
  • .toString()

Exception

  • throw new Exception(value)

Binary Search

  • sorted sequence
  • insertionPoint + 1
  • O(log2(N))

Complexity

  • O(1) // constant
  • O(log2(N)) // logarithmic
  • O(N) // linear
  • O(Nlog2(N)) // log-linear
  • O(N^2) // quadratic
  • O(N^3) // cubic
  • O(2^N) // exponential
  • O(N!)

10/04/2016

###Continuing