String str = "123";
int num = Integer.parseInt(str); // 轉換為int

String str = "3.14";
double num = Double.parseDouble(str); // 轉換為double

String str = "9876543210";
long num = Long.parseLong(str); // 轉換為long

String hexStr = "1A";
int decimal = Integer.parseInt(hexStr, 16); // 十六進制轉十進制 → 26

String binaryStr = "1010";
int decimal = Integer.parseInt(binaryStr, 2); // 二進制轉十進制 → 10

String str = "42";
Integer num = Integer.valueOf(str); // 返回Integer對象
Double d = Double.valueOf("3.1415"); // 返回Double對象

try {
    String input = "12a3";
    int number = Integer.parseInt(input);
} catch (NumberFormatException e) {
    System.out.println("無效的數(shù)字格式: " + e.getMessage());
}

String str = "42.5";
Scanner scanner = new Scanner(str);
double num = scanner.nextDouble(); // 自動識別數(shù)字類型

String str = "12345678901234567890.12345";
BigDecimal bigDecimal = new BigDecimal(str);

// 需要添加依賴：commons-lang3
String str = "123";
if (NumberUtils.isParsable(str)) {
    int num = NumberUtils.toInt(str, 0); // 安全轉換，失敗返回默認值0
}

String str = "  123  ";
int num = Integer.parseInt(str.trim());

NumberFormat format = NumberFormat.getInstance(Locale.US);
Number number = format.parse("1,234,567"); // → 1234567

String str = "123.45";
if (str.matches("-?\\d+(\\.\\d+)?")) {
    // 執(zhí)行轉換操作
}

String hugeNumber = "123456789012345678901234567890";
BigInteger bigInt = new BigInteger(hugeNumber);