java 各种数据类型转换

String str="122.202";
double dnum = Double.parseDouble(str);

// 默认hex 大端字节序
int decimal = Integer.parseInt(hexNumber, 16);

Set<T> mySet = new HashSet<>(Arrays.asList(someArray));

Set<T> mySet = Set.of(someArray);

var mySet = Set.of(someArray);

Double d = new Double(i)

int i = d.intValue();

byte b1 = (byte) 129;
String s1 = String.format("%8s", Integer.toBinaryString(b1 & 0xFF)).replace(' ', '0');
System.out.println(s1); // 10000001

Instant instant = date.toInstant();
ZoneId zoneId = ZoneId.systemDefault();
instant.atZone(zoneId).toLocalDateTime();

    byte[] bytes = ByteBuffer.allocate(4).putInt(i).array();

    public static byte[] int2Bytes(int value) {
        byte[] out = new byte[4];
        for (int i = 0; i < 4; i++) {
            out[i] = (byte) (value >> (8 * (4 - i - 1)));
        }
        return out;
    }

    public static int bytes2Int(byte[] value) {
        int out = 0;
        if (value != null && value.length == 4) {
            for (int i = 0; i < 4; i++) {
                out |= (value[i] & 0xFF) << (8 * (4 - i - 1));
            }
        }
        return out;
    }

   public static long localDateTimeToMills(LocalDateTime localDateTime) {
        ZonedDateTime zdt = localDateTime.atZone(ZoneId.systemDefault());
        return zdt.toInstant().toEpochMilli();
    }

    LocalDate date = LocalDate.now();
    Instant instant = date.atStartOfDay(ZoneId.systemDefault()).toInstant();

LocalDateTime.parse("2022-01-05 15:16", DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm"))

    LocalDateTime.parse(                   // Parse as an indeterminate `LocalDate`, devoid of time zone or offset-from-UTC. NOT a moment, NOT a point on the timeline.
        "04:30 PM, Sat 5/12/2018" ,        // This input uses a poor choice of format. Whenever possible, use standard ISO 8601 formats when exchanging date-time values as text. Conveniently, the java.time classes use the standard formats by default when parsing/generating strings.
        DateTimeFormatter.ofPattern( "hh:mm a, EEE M/d/uuuu" , Locale.US )  // Use single-character `M` & `d` when the number lacks a leading padded zero for single-digit values.
    )                                      // Returns a `LocalDateTime` object.
    .atZone(                               // Apply a zone to that unzoned `LocalDateTime`, giving it meaning, determining a point on the timeline.
        ZoneId.of( "America/Toronto" )     // Always specify a proper time zone with `Contintent/Region` format, never a 3-4 letter pseudo-zone such as `PST`, `CST`, or `IST`. 
    )                                      // Returns a `ZonedDateTime`. `toString` → 2018-05-12T16:30-04:00[America/Toronto].
    .toInstant()                           // Extract a `Instant` object, always in UTC by definition.   

// Get current date time
LocalDateTime currentDateTime = LocalDateTime.now();
// Inbuilt format
static DateTimeFormatter formatter = DateTimeFormatter.ISO_DATE_TIME;
// Custom format
//DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
// Format LocalDateTime
String formattedDateTime = currentDateTime.format(formatter);
//Verify
System.out.println("Formatted LocalDateTime : " + formattedDateTime);       
//Output:
//Formatted LocalDateTime : 2018-07-14T17:45:55.9483536

List list = Arrays.asList(strArray);

        private void testArrayCastToListError() {
                String[] strArray = new String[2];
                List list = Arrays.asList(strArray);
                //对转换后的list插入一条数据
                list.add("1");
                System.out.println(list);
            }
ArrayList<String> list = new ArrayList<String>(Arrays.asList(strArray)) ;

        private void testArrayCastToListRight() {
                String[] strArray = new String[2];
                ArrayList<String> list = new ArrayList<String>(Arrays.asList(strArray)) ;
                list.add("1");
                System.out.println(list);
            }

ArrayList.toArray

Instant foo = Instant.now()
Date.from(foo)