comp305 test1

• write file
• public class HelloApp
• {
•    public static void main(String[] args)
•    {
•       System.out.println("Hello");
•    }
• }
• save file as HelloApp.java
•    same name as class but add .java
• in terminal
• $ javac HelloApp.java  //compiles code
•    HelloApp.class file created
• $java HelloApp  // runs app

• portable
• interpreted --> portable
• compiles to bytecode instead of machine lang.

• custom-compiled bytecode
• Core runtime and additional libraries(JDK JRE)
• JVM
• OS

better memory management

• package comp301a1;
• imports
• public class COMP305A1 {
•    public static void main(String[] args) {
•       //code
•       try {
•      
•       } catch (SQLException ex) {
•          Logger.getLogger(....
•       } catch (IOException ex) {
•          Logger.getLogger(....
•       } // end try-catch
•    } // end main

}

• a  main method.
• It always has the three keywords, public, static, and void.
• Public=method is available to the entire application.
• Static=method can be called directly from the class definition rather than from an instance of the class.
• void=method doesn't return any value.
• also receive an array of strings as an argument or parameter.

• identifier conventions
• identifiers must start with alpha char or _
• conventions:
• class: start with Uppercase
• variables, methods: start with lowercase
• constants: all Uppercase
•    public static final String FIRST = "David";

final meaning once it's been set, it can't be changed.

dereference variables using the keyword null, all lower case. No matter what the scope

• stack faster
• heap more dynamic
• complex objects are stored on heap

That's a keyword that means that this is a member of the class that can be called from the class itself, as opposed to an instance of the class

• Ch3_Packages$ javac ./com/example/java/Main.java
• Ch3_Packages$ java com.example.java.Main Hello "My Friend"

• Java developers typically organize their classes in packages.
• A package is a unique identifier
• that goes at the top of the class declaration.
• But it actually matches a folder hierarchy

• import java.sql.Connection;
• import java.sql.DriverManager;
• Connection connection;
• connection = DriverManager.getConnection(
•      "jdbd:mysql://localhost:3306/dbname"
•    ,"root","mysql");

import java.sql.Statement;

Statement stmt =  connection.createStatement();

• import java.sql.ResultSet;
• ResultSet rs
•     = statement.executeQuery(
•     "SELECT * FROM person");

• while (rs.next())
• {
•    int personId = rs.getInt("personid");
• ...

• import java.util.ArrayList;
• import model.Person;

• ArrayList<Person> personList = new
•     ArrayList<>();

• ResultSet rs = statement.excuteQuery(
•    "select * form person");
• while(rs.next())
• {
•    Person personObj =new Person(
•       rs.getInt("personid"),
•       rs.getString("name"),
•       rs.getString("jobtitle"));
•    personList.add(personObj);
• }

• import model.Person;
• import java.util.HashMap;

• HashMap<Integer,Person> personMap =
•       new HashMap<>();

• for (Person perObj : personList)
• {
•    personMap.put(perObj.getPersonid(),
•                         perObj);
• }

• import java.sql.ResultSet;
• import java.util.HashMap;
• import model.TripType;

• HashMap<Integer, TripType> tripTypeMap
•        = new HashMap<>();

• rs = statement.executeQuery(
•       "select * from triptype");
• while (rs.next())
• {
•    TripType ttObj = new TripType(
•                    rs.getTripTypeId("triptypeid"),
•                    rs.getString("name"),
•                    rs.getDesc("description"));
•    tripTypeMap.put(ttObj.getTripTypeId(),
•                         ttObj);
• }

import java.io.File;

File file = new File("srchtmltripinfo.html");

• import java.io.FileWriter;
• import java.io.BufferedWriter;

• FileWriter fw
•       = new FileWriter(fileName);
• BufferedWriter bw
•       = new BufferedWriter(fw);
• String fileData = "some info";
• bw.write(fileData);
• bw.close();

• package model;
• public class Person {
•    private int personid;
•    private String name;
•    public Person(int personid, String name)
•    {
•       this.personid = personid;
•       this.name = name;
•    }

• package model;
• public class Person
• {
•    ...
•    public String getName() {return name;}

•    public void setName(String name)
•    {
•       this.name = name;
•    }
•    ...
• }

• @Override
• public String toString()
• {
•    return personid + ", " + name;
• }

• import javal.text.SimpleDateFormat;
• import java.util.Date;

• Date depdate = rs.getDate("depdate");
• SimpleDateFormat df
•    =new SimpleDateFormat("MMM d, yyyy");
• System.out.println(df.formate(date));

• import java.io.IOException;
• import java.sql.SQLException;
• import java.util.logging.Level;
• import java.util.logging.Logger;

• catch (SQLException ex)
• {            Logger.getLogger(COMP305A1.class.getName()) .log(Level.SEVERE, null, ex);
• }
• catch (IOException ex)
• {            Logger.getLogger(COMP305A1.class.getName())                    .log(Level.SEVERE, null, ex);       
• }

• String last = person.getName().split(",")[0];
• String first = person.getName().split(",")[1].trim();

• String sentence = "This is a sentence.";
• String[] wordArray = sentence.split(" ");
• for ( String word : wordArray)
• {
•             System.out.println(word);
• }

• try {                    }
• catch (Exception e) {        }

• Scanner scanner = new Scanner(System.in);
• input =scanner.nextLine();
• Double hours = Double.parseDouble(input.split(",")[0].trim());

• char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
• String helloString = new String(helloArray);
• System.out.println(helloString);

• String palindrome = "Dot saw I was Tod";
• int len = palindrome.length();
• char[] tempCharArray = new char[len];
• char[] charArray = new char[len];
• for (int i = 0; i < len; i++)
• {
•     tempCharArray[i] = palindrome.charAt(i);
• }
• for (int j = 0; j < len; j++)
• {
•     charArray[j] =tempCharArray[len - 1 - j];
• }
• String reversePalindrome
•    = new String(charArray);
• System.out.println(reversePalindrome);

• String fs;
• fs = String.format(
•    "The value of the float "
•    + "variable is %f, while "
•    + "the value of the "
•    + "integer variable is %d, "
•    + " and the string is %s",
•     floatVar, intVar, stringVar);
• System.out.println(fs);

• int i = 5;
• String s2 = String.valueOf(i);

• double d = 858.48;
• String s = Double.toString(d);

• float a = Float.parseFloat(args[0]);
• float b = Float.parseFloat(args[1]);

• import java.text.SimpleDateFormat;
• import java.util.Date;
• Date date = new Date();
• SimpleDateFormat df
•      = new SimpleDateFormat(
•        "MMM d, yyyy");
• System.out.println(df.format(date));

• SimpleDateFormat df2
•    = new SimpleDateFormat(
•     "MM/dd/yyyy hh:mm:ss");        System.out.println(df2.format(date));