java練習

ConnectWeb.java

import java.io.*;
import java.net.*;

public class ConnectWeb{
    public static void main(String[] args){
        http();
        https();
    }
    static void https(){//https目前還是不行，試過網路上的code失敗
        String target = "https://gist.githubusercontent.com/Benjamin1021523/1701eb96206b779e1595ce0cc3f82466/raw/fc71033195bdec93457f39fe26cbef74701dcce2/Example.java";
    }
    static void http(){
        String target = "http://127.0.0.1:5000/show/";
        try{
            URL url = new URL(target);
            InputStream stream = url.openStream();
            String content = readAll(stream, "UTF-8");
            System.out.print(content);
        }
        catch(Exception e){
            System.out.println(e);
        }
    }
    static String readAll( InputStream stream, String charcode ) throws IOException{
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(stream, charcode)
        );
        StringBuilder sb = new StringBuilder();
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line+"\n");
        }
        return sb.toString();
    }
}

Example.java

import java.util.*;

public class Example{
    public static void main(String[] args){
        List<Integer> a = new ArrayList<Integer>();
        for(int i = 0;i < 5;i++)    a.add(i);
        List<Integer> b = a;
        for(int i:a)    System.out.print(i + " ");
        System.out.println();
        for(int i:b)    System.out.print(i + " ");
        System.out.println();
    }
}
//b初始化時使用了和a同樣的一塊記憶體
//就像linux指令的ln -h一樣

PrimeNumber.java

//印出1~10000間的質數
public class PrimeNumber{
    public static void main(String[] args){
        int n = 9974;//No prime number in 9974 ~ 10000
        boolean[] arr = new boolean[n];
        for(int i = 2;i < n;i++){
            if(!arr[i]){
                for(int j = i+i;j < n;j += i){
                    arr[j] = true;
                }
            }
        }
        int cnt = 0;
        for(int i = 2;i < n;i++){
            if(!arr[i]){
                System.out.printf(i + " ");
                ++cnt;
                if(cnt % 10 == 0)   System.out.println();
            }
        }
        System.out.println();
    }
}

ReadFile.java

//單純的讀檔印出，使用個物件還要自己在以外的地方加throws真是麻煩
import java.io.*;
public class ReadFile{
    public static void main(String[] args) throws IOException{
        String name = "Example.java";
        String charset = "utf8";
        BufferedReader reader = new BufferedReader(
            new InputStreamReader(
                new FileInputStream(name),
                charset
            )
        );
        String Line;
        while((Line = reader.readLine()) != null){
            System.out.println(Line);
        }
    }
}