Eclipse 安裝與設定 for CentOS 8

目標設定

• 在 CentOS 8 linux 中安裝 Eclipse

Eclipse 安裝流程

1. 下載套件
   • Eclipse 官方網站
     
   • 下載目前最新的套件！
     
2. 將檔案解壓縮至 /opt 目錄下

   $ tar zxvf eclipse-inst-jre-linux64.tar.gz -C /opt/
   $ cd /opt/eclipse-installer
   

3. 執行安裝工作：

   $ ./eclipse-inst
   

   • 選擇安裝項目：
     
   • 指定工作目錄後，進行安裝工作
     
   • 同意授權！
     
   • 安裝流程
     
   • 安裝結束，可直接啟動！
     
4. 啟動時，選擇工作目錄
   
5. 出現歡迎畫面！
   
6. 操作畫面
   

VSCode 基本安裝與 Java 套件的使用

VSCode 安裝

1. 下載網址：
   • Visual Studio Code 官方網站
     • Windows 10:下載 Windows X86 stable 版本
     • CentOS 8:點選 Linux x86 .rpm 版本
2. 執行安裝工作！
   • Windows 10:點擊下域的檔案，即可執行安裝工作，可一鍵執行完成！
   • CentOS 8:按照說明文件內容，使用 yum 進行安裝即可！

VSCode 設定

1. 開啟 VSCode
2. 執行 Extensions
3. 輸入 Java
4. 選擇 Java Extension Pack 後，按下 install 按鍵：
   
   這個套件一口氣會協助安裝六個套件：
   • Visual Studio IntelliCode
   • Language Support for Java(TM) by Red Hat
   • Debugger for Java
   • Java Test Runner
   • Maven for Java
   • Project Manager for Java
5. 直接使用瀏覽器查看！

建立 Java SE project

1. 使用 Ctrl+Alt+p 開啟命令列！
　
2. 輸入並選擇 Java: Create Java Project...
   
3. 選擇 No build tools 項目
   
4. 選擇存放專案的資料夾
   
5. 輸入專案名稱
   
6. 查看專案內容
   
7. 如果沒有安裝 JDK 或是 OpenJDK ，可以利用此時進行安裝的工作：
   
8. 按下「Get the Java Development Kit」按鍵，將連至 Red Hat Developer 官方網站
   
9. 若是 Windows 10 的使用者，可在 Red Hat Developer 網站中，下載 OpenJDK 相關套件，並且安裝！
   
   
10. CentOS 8 的使用者，可以利用 yum 進行安裝工作：

    # yum install java-latest-openjdk java-latest-openjdk-devel
    # alternatives --config java
    (選擇java-latest-openjdk.x86_64)
    # javac --version
    

11. 選擇視窗左下角的 Manager 項目：
    
12. 選擇 setting 項目：
    
13. 輸入 java.runtime 找出 Java>Configuration:Ｒuntimes 項目，進行 settings.json 檔案的編輯：
    
14. 輸入下列資料，並且存檔：
    
15. 切換回 setting 項目，選擇 Workspace 選項，輸入 java.home 關鍵字後，編輯 Java:Home 的 settings.jason 檔案：
    
16. 編寫內容如下：
    
17. 重新執行專案，分別按下右上的兩個按鍵，查看結果：
    

建立 Java EE project

1. 安裝 Apache Tomcat 9，CentOS 8 可參考這一篇！Windows 10 可參考這一篇！
2. 在工作目錄/專案目錄底下，找到 .classpath 檔案，加入下列設定：

     <classpathentry kind="lib" path="/opt/tomcat/apache-tomcat-9.0.44/lib/servlet-api.jar"/>
   

3. 重新啟動 vscode 測試！

相關資料索引
參考文獻：

1. 使用 VSCode 進行 Java SE/EE 開發

Java 的 Thread 基本應用

繼承 Thread :

public class ExampleThread extends Thread{
    @Override
    public void run() {
        for(int i = 0; i<100; i++){
            System.out.println("i: " + i);
        }
    }
}

public class Demo {
    public static void main(String[] args){
        ExampleThread t1 = new ExampleThread();
        t1.start();
    }
}

執行 Runnable 介面 :

public class ExampleRunnable implements Runnable{

    @Override
    public void run() {
        for(int i = 0; i<100; i++){
            System.out.println("i: " + i);
        }
    }  
}

public class RunnableDemo {
     public static void main(String[] args){
        ExampleRunnable r1 = new ExampleRunnable();
        Thread t1 = new Thread(r1);
        t1.start();
    }
}

Java 檔案管理程式

NIO.2 基本應用：

import java.nio.file.Path;
import java.nio.file.Paths;

public class NIODemo {
    public static void main(String[] args){
        Path p1 = Paths.get("C:\\workspace\\test\\test1\\hello.text");
        System.out.println("Get File Name: " + p1.getFileName());
        System.out.println("Get Parent: " + p1.getParent());
        System.out.println("Get Name Count: " + p1.getNameCount());
        System.out.println("Get Root:" + p1.getRoot());
        System.out.println("Is Absolute:" + p1.isAbsolute());
        System.out.println("To Absolute Path:" + p1.toAbsolutePath());
        System.out.println("To URI Path:" + p1.toUri());
    }
}

Serializable 的應用

範例：

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.Serializable;

public class Stock implements Serializable{
    private static final long serialVersionUID = 100L;
    private String symbol;
    private int shares;
    private double purchasePrice;
    private transient double currPrice;

    public Stock(String symbol, int shares, double purchasePrice) {
        this.symbol = symbol;
        this.shares = shares;
        this.purchasePrice = purchasePrice;
        setStockPrice();
    }
    
    private void setStockPrice() {
        this.currPrice = this.purchasePrice;
    }
     
    private void readObject(ObjectInputStream ois) throws ClassNotFoundException, IOException{
        ois.defaultReadObject();
        setStockPrice();
    }
}

import java.io.FileInputStream;
import java.io.Serializable;
import java.util.Set;

public class Portfolio implements Serializable{
    public transient FileInputStream inputFile;
    public static int BASE = 100;
    private transient int totalValue = 10;
    private Set stocks;
 
    Portfolio(Stock s1, Stock s2, Stock s3) {
        this.stocks.add(s1);
        this.stocks.add(s2);
        this.stocks.add(s3);
    }  
}

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Demo {
    public static void main(String[] args){
    
        Stock s1 = new Stock("ORCL",100, 32.5);
        Stock s2 = new Stock("AOOL",100, 245);
        Stock s3 = new Stock("GOGL",100, 54.67);
        
        Portfolio p = new Portfolio(s1,s2,s3);
        
        try(FileOutputStream fos = new FileOutputStream(args[0]);
            ObjectOutputStream out = new ObjectOutputStream(fos)){
            out.writeObject(p);
        } catch (IOException ex) {
           System.out.println("Exception writing out Portfolio :" + ex);
        }
        
        try(FileInputStream fis = new FileInputStream(args[0]);
            ObjectInputStream in = new ObjectInputStream(fis)){
            Portfolio newP = (Portfolio)in.readObject();
        } catch (ClassNotFoundException | IOException ex) {
           System.out.println("Exception reading in Portfolio :" + ex);
        }
    }
}

I/O Chain 的練習

Buffer 與 File 的 Chain :

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class ChainDemo {
    public static void main(String[] args){
        try(BufferedReader bufInput = new BufferedReader(new FileReader(args[0]));
            BufferedWriter bufOutput = new BufferedWriter(new FileWriter(args[1]))){
            String line = "";
            while ((line = bufInput.readLine()) != null){
                bufOutput.write(line);
                bufOutput.newLine();
            }
        }   catch (FileNotFoundException ex) {
            System.out.println("File not found!");
        } catch (IOException ex) {
            System.out.println("I/O Error");
        }  
    }
}

InputStream 與 OutputStream

Byte 種類的 I/O 處理：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;

public class StreamDemo {
    public static void main(String[] args){
        byte[] data = new byte[128];
        int dataLen = data.length;
        
        try(FileInputStream fis = new FileInputStream(args[0]);
            FileOutputStream fos = new FileOutputStream(args[1])){
            System.out.println("Bytes available: " + fis.available());
            int count = 0;
            int read = 0;
            while ((read = fis.read(data)) != -1){
                if (read < dataLen) 
                    fos.write(data,0,read);
                else
                    fos.write(data);
                count += read;
            }
            System.out.println("Wrote: " + count);
        }   catch (FileNotFoundException ex) {
            System.out.println("File not Found! " + ex);
        } catch (IOException ex) {
            System.out.println("I/O Error! " + ex);
        }
    }
}

Assertion 用法

import java.util.Scanner;

public class Demo {
    public static void main(String[] args){
    
        Scanner scanner = new Scanner(System.in);
        System.out.print("Please input positive number:");
        int input = scanner.nextInt();
        if (input > 0){
            System.out.println("Number: " + input);
        } else {
            assert (input > 0): "執行有誤....";
            System.out.println("Error : " + input);
        }
    }
}

Java 例外處理--AutoCloseable

有 catch 敘述：

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

public class OpenFileDemo{
  public static void main(String[] args){
    System.out.println("About to open a file...");
    
    try (InputStream in = new FileInputStream("hello.txt")){
      System.out.println("File is opened..");
      int data = in.read();
    } catch (FileNotFoundException e){
        System.out.println(e.getMessage());
    } catch (IOException e){
        System.out.println(e.getMessage());
    }
  }
}

沒有 catch 敘述(利用 throws，丟給上頭去傷腦筋...)

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;

public class ThrowDemo {
    public static void main(String[] args){
        try {    
            int data = readByteFromFile();
        } catch (IOException ex) {
            System.out.println(ex.getMessage());
        }
    }

    private static int readByteFromFile() throws FileNotFoundException, IOException {
        try(InputStream in = new FileInputStream("a.txt")){
            System.out.println("File is opening...");
            return in.read();
        }
    }
}

正規化表示式

Pattern & Matcher 的應用：

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class RegxDemo {
    public static void main(String[] args){
    
        String test = "He was a teacher";
        
        Pattern p1 = Pattern.compile("w.s");
        Matcher m1 = p1.matcher(test);
        if (m1.find()){
            System.out.println("Found: " + m1.group());
        }
        
        Pattern p2 = Pattern.compile("w[abc]s");
        Matcher m2 = p2.matcher(test);
        if (m2.find()){
            System.out.println("Found: " + m2.group());
        }
        
        Pattern p3 = Pattern.compile("t[^xyz]acher");
        Matcher m3 = p3.matcher(test);
        if (m3.find()){
            System.out.println("Found: " + m3.group());
        }

        String header = "<h1>Hello World<h1>";
        Pattern p4 = Pattern.compile("h1");
        Matcher m4 = p4.matcher(header);
        if (m4.find()){
            System.out.println("Found: " + m4.group());
            header = m4.replaceAll("p");
            System.out.println(header);
        }  

    }
}

Scanner 切割字串的應用

import java.util.Scanner;

public class ScannerDemo {
    public static void main(String[] args){
        StringBuilder sb = new StringBuilder(64);
        String test = "1.1, 2.2, 3.3";
        float fsum = 0.0f;
        
        Scanner s = new Scanner(test).useDelimiter(", ");
        while(s.hasNextFloat()){
            float f = s.nextFloat();
            fsum += f;
            sb.append(f).append(" ");
        }
        System.out.println("Values for: " + sb.toString());
        System.out.println("FSum: " + fsum);
    }
}

StringBuilder 用法

import java.io.PrintWriter;
import java.util.StringTokenizer;

public class StringDemo {
    public static void main(String[] args){
        
        //StringBuilder 範例
        StringBuilder sb = new StringBuilder(500);
        
        sb.append(", this is a good day!");
        sb.insert(0,"Today is Friday!");
        for (int i = 1; i< 11 ; i++){
            sb.append(i).append("    ");
        }
        sb.append("] times");
        System.out.println(sb.toString());
        System.out.println();
        
        //String Methods 範例
        PrintWriter pw = new PrintWriter(System.out, true);
        String tc01 = "It was the best of times";
        String tc02 = "It was the worst of times";
        
        if (tc01.equals(tc02)){
            pw.println("Strings match...");
        }
        if (tc01.contains("It was")){
            pw.println("It was found");
        }
        String temp = tc02.replace("w", "zw");
        pw.println(temp);
        pw.println(tc02.substring(5, 12));
         pw.println();
         
        //String Split 範例
        String shirts = "Blue Shirt, Red Shirt, Black Shirt, Maroon Shirt";
        
        String[] results = shirts.split(", ");
        for (String shirtStr:results){
            pw.println(shirtStr);
        }
         pw.println();
         
        //Tokenizer 範例
        StringTokenizer st = new StringTokenizer(shirts, ", ");
        while(st.hasMoreTokens()){
            pw.println(st.nextToken());
        }
    }
}

Properties 的使用

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.Properties;

public class Demo1 {
    public static void main(String[] args) throws FileNotFoundException{
    
        Properties myProps = new Properties();
        try{
            FileInputStream fis = new FileInputStream("C:\\ServerInfo.properties");
            myProps.load(fis);
        } catch (IOException e){
            System.out.println("Error: " + e.getMessage());
        }
        
        System.out.println("Server: " + myProps.getProperty("hostName"));
        System.out.println("User: " + myProps.getProperty("userName"));
        System.out.println("Password: " + myProps.getProperty("password"));
           
    }
}

Properties 的檔案內容：

hostName=www.example.com
userName=user
password=pass

Comparator 的用法

Comparator 的用法：

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class ComparatorDemo {
    public static void main(String[] args){
    
        List<Student> studentList = new ArrayList<>(3);
        Comparator<Student> sortName = new StudentSortName();
        Comparator<Student> sortGpa = new StudentSortGpa();
        
        studentList.add(new Student("Thomas Jefferson", 1111, 3.8));
        studentList.add(new Student("John Adams", 2222, 3.9));
        studentList.add(new Student("George Washington", 3333, 3.4));
        
        Collections.sort(studentList, sortName);
        for (Student student : studentList){
            System.out.println(student.getName());
        }
         Collections.sort(studentList, sortGpa);
        for (Student student : studentList){
            System.out.println(student.getGpa());
        }
    }
}

public class Student {
private String name;
    private long id = 0;
    private double gpa = 0;
            
    public Student(String name, long id, double gpa) {
        this.name = name;
        this.id = id;
        this.gpa = gpa;
    }

    public String getName() {
        return name;
    }

    public double getGpa() {
        return gpa;
    }
}

import java.util.Comparator;

public class StudentSortName implements Comparator<Student> {

    public StudentSortName() {
    }

    @Override
    public int compare(Student o1, Student o2) {
        int result = o1.getName().compareTo(o2.getName());
        if (result != 0){return result;}
        else { return 0;}
    }
}

import java.util.Comparator;

public class StudentSortGpa implements Comparator<Student> {

    public StudentSortGpa() {
    }

    @Override
    public int compare(Student o1, Student o2) {
        if (o1.getGpa() < o2.getGpa()){return 1;}
        else if (o1.getGpa() > o2.getGpa()){ return -1;}
        else {return 0;}
    }
}

Comparable 的用法

Comparable 的用法：

public class ComparableStudent implements Comparable<ComparableStudent>{
    private String name;
    private long id = 0;
    private double gpa = 0.0;

    public ComparableStudent(String name, long id, double gpa) {
        this.name = name;
        this.id = id;
        this.gpa = gpa;
    }

    public String getName() {
        return name;
    }
        
    @Override
    public int compareTo(ComparableStudent o) {
        int result = this.name.compareTo(o.getName());
        if (result > 0){return 1;}
        else if (result < 0){return -1;}
        else {return 0;}
    }
}

Demo 程式：

import java.util.Set;
import java.util.TreeSet;

public class Demo {
    public static void main(String[] args){
        Set<ComparableStudent> studentList = new TreeSet<>();
        
        studentList.add(new ComparableStudent("Thomas Jefferson", 1111, 3.8));
        studentList.add(new ComparableStudent("John Adams", 2222, 3.9));
        studentList.add(new ComparableStudent("George Washington", 3333, 3.4));
         
         for (ComparableStudent student : studentList){
             System.out.println(student.getName());
         }
    }
}

Queue 的應用

import java.util.ArrayDeque;
import java.util.Deque;

public class NewClass {
    public static void main(String[] args){
    
        Deque<String> stack = new ArrayDeque<>();
        stack.push("One");
        stack.push("Two");
        stack.push("Three");
        
        int size = stack.size() -1;
        while(size >= 0){
            System.out.println(stack.pop());
        }
    }
}

Map 應用

import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class MapDemo {
    public static void main(String[] args){
    
        Map<String, String> shirtList = new TreeMap<>();
        shirtList.put("S001", "Blue Shirt");
        shirtList.put("S002", "Black Shirt");
        shirtList.put("S003", "Gray Shirt");
        
        Set<String> keys = shirtList.keySet();
        System.out.println("====== Shirt List ======");
        for (String key : keys){
            System.out.println("Part#: " + key + " " 
                               + shirtList.get(key));
        } 
    }
}

Set 應用

某家公司的面試題目：

import java.util.Set;
import java.util.TreeSet;
import java.util.Scanner;

public class SetDemo {
    public static void main(String[] args){
    
        Set<Integer> num = new TreeSet<>();
        Scanner scanner = new Scanner(System.in);
        Integer[] b = new Integer[3];
        for (int i = 0; i < 3 ;  i++){
            System.out.print("Please the eage's length: ");
            num.add(scanner.nextInt());
        }
        num.toArray(b);
        if (b[2] < (b[0]+b[1])){
        switch (num.size()){
            case 1: 
                System.out.println("正三角形");
                break;
            case 2:
                System.out.println("等腰三角形");
                break;
            case 3:
                if (triangle(b)){
                    System.out.println("直角三角形");
                } else {
                    System.out.println("其他種類三角形");
                }
        }
        } else {
             System.out.println("無法構成三角形");
        }
    }

    private static boolean triangle(Integer[] b) {
        if ((b[2] * b[2]) == (b[0]*b[0] + b[1]*b[1])){
          return true;
        } else {
            return false;
        }
    }
}

Boxing & UnBoxing

AutoBoxing 與 Auto Unboxing:

public class AutoBox {
    public static void main(String[] args){
    
        Integer intObject = new Integer(1);
        int intPrimitive = 2;
        
        Integer tempInteger;
        int tempPrimitive;
        
        tempInteger = new Integer(intPrimitive);
        tempPrimitive = intObject.intValue();
        
        tempInteger = intPrimitive;  //Auto Boxing
        tempPrimitive = intObject; // Auto Unboxing
    }
}

收集器：ArrayList & List

Collection 利用 Generic 來實作的好處：

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class ArrayListDemo {
    public static void main(String[] args){
    
        List partList = new ArrayList<>();
        partList.add(new Integer(1111));
        partList.add(new Integer(2222));
        partList.add(new Integer(3333));
        partList.add("Hello World");  //Compile Error : Not Integer
        
        // 利用 Iterator 來遍訪 ArrayList 內的 elements 
        Iterator elements = partList.iterator();  
        while (elements.hasNext()){
            Integer partNumberObject = elements.next();
            int partNumber = partNumberObject.intValue();
            
            System.out.println("Part Number: " + partNumber);
        }
    }
}