Java基础

@Data
public class BasicTest {

    /**
     * 参数检验
     *
     * @param a
     */
    @Test
    void testArg(String a) {
        if (a == null) {
            throw new NullPointerException("参数a为空");
        }
        if (a == "") {
            throw new IllegalArgumentException("参数异常");
        }
    }

    /**
     * 二进制和十进制转换
     */
    @Test
    void testBinaryString() {
        int i = 100;
        String s = Integer.toBinaryString(i);
        System.out.println(s);
        System.out.println(Integer.parseInt(s, 2));
    }

    /**
     * 连续两次异或还是自己
     */
    @Test
    void testTwoAction() {
        int i = (6 ^ 3) ^ 3;
        System.out.println(i);
    }


    /**
     *         00000110
     *     &    00000011
     * ------------------
     *      00000010
     */
    @Test
    public void test与(){
        int a=6&3;
        System.out.println(a);  //2
        System.out.println(Integer.toBinaryString(a));  //10
    }

    /**
     *         00000110
     *     |    00000011
     * ------------------
     *      00000111
     */
    @Test
    public void test或(){
        int a=6|3;
        System.out.println(a); //7
        System.out.println(Integer.toBinaryString(a));  //111
    }

    /**   相同为false，不同为true
     *         00000110
     *     ^    00000011
     * ------------------
     *      00000101
     */
    @Test
    public void test异或(){
        int a=6^3;
        System.out.println(a); //5
        System.out.println(Integer.toBinaryString(a));  //101
    }


    /**
     * 取反的规则
     *
     * 先取反 +6变-6
     *        -7变+7
     * 然后都减-1
     */
    @Test
    public void test取反(){
        System.out.println(~6);  //-7
        System.out.println(~-7);  //6
    }


    /**
     *  -6在计算机的表示原理
     *
     *  00000110  先得到+6的2进制表示
     *  11111001  取反
     *  11111010  再加1
     *
     *  ----------------------
     *
     *  11111001 先-1
     *  00000110 取反后，得到+6
     *  再加上-号，那么就是-6
     */
    @Test
    public void test负数表示(){
        String s = Integer.toBinaryString(-6);
        System.out.println(s);
    }

    /**
     * 2*3
     */
    @Test
    public void test移位运算(){
        System.out.println(2<<3); //16  2*(2^3)
        System.out.println(16>>3); //2  16/(2^3)
        System.out.println(-16>>3); //-2
    }

    @Test
    public void test不引用三方变量对两个数进行交换(){
        int a=5;
        int b=10;
        a=a^b;
        b=a^b;  //(a^b)^b=a
        a=a^b;  //(a^b)^a=(b^a)^a=b
        System.out.printf("%d,%d",a,b);
    }

    @Test
    void testEncrypt() throws IOException {

        ClassPathResource classPathResource = new ClassPathResource("1.png");
        String path = classPathResource.getFile().getPath();
        System.out.println(path);
        FileInputStream fileInputStream = new FileInputStream(path);
        FileOutputStream fileOutputStream = new FileOutputStream(path.replace("1.png","2.png"));
        int content=-1;
        while ((content=fileInputStream.read())!=-1){
            fileOutputStream.write(content^5);
        }
        fileOutputStream.close();
        fileInputStream.close();
        System.out.println("encrypt finished");
    }

    @Test
    void testDecrypt() throws IOException {
        ClassPathResource classPathResource = new ClassPathResource("2.png");
        String path = classPathResource.getFile().getPath();
        System.out.println(path);
        FileInputStream fileInputStream = new FileInputStream(path);
        FileOutputStream fileOutputStream = new FileOutputStream(path.replace("2.png","3.png"));
        int content=-1;
        while ((content=fileInputStream.read())!=-1){
            fileOutputStream.write(content^5);
        }
        fileOutputStream.close();
        fileInputStream.close();
        System.out.println("decrypt finished");
    }

    @Test
    void testBase64() throws UnsupportedEncodingException {
        String a="hello";
        byte[] encode = Base64.getEncoder().encode(a.getBytes(StandardCharsets.UTF_8));
        byte[] decode = Base64.getDecoder().decode(encode);
        String s = new String(decode, StandardCharsets.UTF_8);
        System.out.println(s);
    }

    @Test
    void testDate() {
        LocalDateTime now = LocalDateTime.now();
        DateTimeFormatter dateTimeFormatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String format = now.format(dateTimeFormatter);
        System.out.println(format);

        long l = System.currentTimeMillis();
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String format1 = simpleDateFormat.format(l);
        System.out.println(format1);
    }

    @Test
    void testRandom(){
        char[] array={'1','2','3','4','5','6','你','中','我','国'};
        Random random = new Random();
        StringBuilder stringBuilder = new StringBuilder();
        for(int i=0;i<4;i++){
            int i1 = random.nextInt(array.length);
            stringBuilder.append(array[i1]);
        }
        System.out.println(stringBuilder.toString());
    }

    @Test
    void testRuntime() throws Exception {
        Runtime runtime = Runtime.getRuntime();
        System.out.println("可用内存:"+runtime.freeMemory());
        System.out.println("获取JVM最大使用内存"+runtime.maxMemory());
        System.out.println("获取JVM只能使用内存"+runtime.totalMemory());

        Process notepad = runtime.exec("notepad");
        Thread.sleep(3000);
        notepad.destroy();
    }

    @Test
    void runShello() {
        String pathOrCommand="";
        List<String> result = new ArrayList<>();

        try {
            // 执行脚本
            Process ps = Runtime.getRuntime().exec(pathOrCommand);
            int exitValue = ps.waitFor();
            if (0 != exitValue) {
                System.out.println("call shell failed. error code is :" + exitValue);
            }

            // 只能接收脚本echo打印的数据，并且是echo打印的最后一次数据
            BufferedInputStream in = new BufferedInputStream(ps.getInputStream());
            BufferedReader br = new BufferedReader(new InputStreamReader(in));
            String line;
            while ((line = br.readLine()) != null) {
                System.out.println("脚本返回的数据如下： " + line);
                result.add(line);
            }
            in.close();
            br.close();

        } catch (Exception e) {
            e.printStackTrace();
        }

        System.out.println(result.toString());
    }

    @Test
    public void testArrayCopy(){
        int[] src={10,12,14,16,19};
        int[] dest=new int[4];

        System.arraycopy(src, 0, dest, 2, 2);
        System.out.println(Arrays.toString(dest));  //[0,0,10,12]
    }

    @Test
    void testSystemEnv() {
       /* Map<String, String> getenv = System.getenv();
        for (Map.Entry<String, String> stringStringEntry : getenv.entrySet()) {
            System.out.println(stringStringEntry.getKey()+":"+stringStringEntry.getValue());
        }*/
        String java_home = System.getenv("JAVA_HOME");
        System.out.println("java_home:"+java_home);

        Properties properties = System.getProperties();
        properties.list(System.out);
    }

    /**
     * substring包头不包尾
     * endIndex实际为endIndex+1;
     */
    @Test
    public  void testStringSubstring() {
        String a="hello,china";
        System.out.println(a.substring(0,5));  //hello
        System.out.println(a.substring(1,5));   //ello,所谓的endIndex实际上是长度
    }


    /**
     *
     *  String()  创建一个空内容 的字符串对象。
     String(byte[] bytes)  使用一个字节数组构建一个字符串对象
     String(byte[] bytes, int offset, int length)
     bytes :  要解码的数组
     offset： 指定从数组中那个索引值开始解码。
     length：　要解码多个元素。

     String(char[] value)  使用一个字符数组构建一个字符串。
     String(char[] value, int offset, int count)  使用一个字符数组构建一个字符串， 指定开始的索引值，与使用字符个数。
     String(int[] codePoints,int offset,int count)
     String(String original)
     */
    @Test
    public void testStringConstructor() {

        String str = null;
        String src="你好中国";

        //转bytes()
        byte[] bytes = src.getBytes();
        str=new String(bytes,0,2);
        System.out.println(str);   //你

        //转charArray()
        char[] charArray = src.toCharArray();
        str=new String(charArray,1,3);
        System.out.println(str);  //好中国

    }