3.1分解字元串
String a = "Java is great";
System.out.println(a);
String b = a.substring(5);
System.out.println(b);
String c = a.substring(5, 7);
System.out.println(c);
String d = a.substring(5, a.length());
System.out.println(d); 3.3字元串分隔連接配接
//final String SAMPLE_STRING = "Alpha Bravo Charlie";
final String SAMPLE_STRING = "喜 歡 我";
StringBuilder sb1 = new StringBuilder();
for (String word : SAMPLE_STRING.split(" ")) {
if (sb1.length() > 0) {
sb1.append(", ");
}
sb1.append(word);
}
System.out.println(sb1);
// Method using a StringTokenizer
StringTokenizer st = new StringTokenizer(SAMPLE_STRING);
StringBuilder sb2 = new StringBuilder();
while (st.hasMoreElements()) {
sb2.append(st.nextToken());
if (st.hasMoreElements()) {
sb2.append(", ");
}
}
System.out.println(sb2); 3.5字元串對齊
public enum Justify {LEFT,CENTER,RIGHT}
private Justify just;
private int maxChars;
public StringAlign(int maxChars, Justify just) {
switch(just) {
case LEFT:
case CENTER:
case RIGHT:
this.just = just;
break;
default:
throw new IllegalArgumentException("invalid justification arg.");
}
if (maxChars < 0) {
throw new IllegalArgumentException("maxChars must be positive.");
}
this.maxChars = maxChars;
}
@Override
public StringBuffer format(
Object input, StringBuffer where, FieldPosition ignore) {
String s = input.toString();
String wanted = s.substring(0, Math.min(s.length(), maxChars));
switch (just) {
case RIGHT:
pad(where, maxChars - wanted.length());
where.append(wanted);
break;
case CENTER:
int toAdd = maxChars - wanted.length();
pad(where, toAdd/2);
where.append(wanted);
pad(where, toAdd - toAdd/2);
break;
case LEFT:
where.append(wanted);
pad(where, maxChars - wanted.length());
break;
}
return where;
}
protected final void pad(StringBuffer to, int howMany) {
for (int i=0; i<howMany; i++)
to.append(' ');
}
String format(String s) {
return format(s, new StringBuffer(), null).toString();
}
public Object parseObject (String source, ParsePosition pos) {
return source;
}
public static void main(String[] args) {
System.out.println(new StringAlign(150,Justify.RIGHT).format("String Align"));
} 3.6Unicode字元和String之間的轉換
StringBuilder b = new StringBuilder();
for (char c = 'a'; c<'d'; c++) {
b.append(c);
}
b.append('\u00a5');
b.append('\u01FC');
b.append('\u0391');
b.append('\u03A9');
for (int i=0; i<b.length(); i++) {
System.out.printf(
"Character #%d (%04x) is %c%n",
i, (int)b.charAt(i), b.charAt(i));
}
System.out.println("Accumulated characters are " + b); 3.7字元串颠倒
String s = "煩 躁";
Stack<String> myStack = new Stack<>();
StringTokenizer st = new StringTokenizer(s);
st.countTokens();
while (st.hasMoreTokens()) {
myStack.push(st.nextToken());
}
System.out.print('"' + s + '"' + "\n backwards by word is:\n\t\"");
while (!myStack.empty()) {
System.out.print(myStack.pop());
System.out.print(' ');
}
System.out.println('"'); 3.9控制字母大小寫
String name = "Java Cookbook";
System.out.println("Normal:\t" + name);
System.out.println("Upper:\t" + name.toUpperCase());
System.out.println("Lower:\t" + name.toLowerCase()); 3.10縮排文本文檔
protected int nSpaces;
Undent(int n) {
nSpaces = n;
}
public static void main(String[] av) throws Exception {
Undent c = new Undent(5);
switch (av.length) {
case 0:
c.process(new BufferedReader(
new InputStreamReader(System.in)));
break;
default:
for (int i = 0; i < av.length; i++)
try {
c.process(new BufferedReader(new FileReader(av[i])));
} catch (FileNotFoundException e) {
System.err.println(e);
}
}
}
public void process(BufferedReader is) throws Exception{
String inputLine;
while ((inputLine = is.readLine()) != null) {
int toRemove = 0;
for (int i = 0; i < nSpaces && i < inputLine.length() &&
Character.isWhitespace(inputLine.charAt(i)); i++)
++toRemove;
System.out.println(inputLine.substring(toRemove));
}
is.close(); 3.11輸入非列印字元
System.out.println("Java Strings in action:");
System.out.println("An alarm entered in Octal: \007");
System.out.println("A tab key: \t(what comes after)");
System.out.println("A newline: \n(what comes after)");
System.out.println("A UniCode character: \u0207");
System.out.println("A backslash character: \\"); 4.3找到比對的文本
String patt = "Q[^u]\\d+\\.";
Pattern r = Pattern.compile(patt);
String line = "Order QT300. Now!";
Matcher m = r.matcher(line);
if (m.find()) {
System.out.println(patt + " matches \"" +
m.group(0) +
"\" in \"" + line + "\"");
} else {
System.out.println("NO MATCH");
} 4.4替換比對的文本
String patt = "\\bfavor\\b";
String input = "Do me a favor? Fetch my favorite.";
System.out.println("Input: " + input);
Pattern r = Pattern.compile(patt);
Matcher m = r.matcher(input);
System.out.println("ReplaceAll: " + m.replaceAll("favour"));
m.reset();
StringBuffer sb = new StringBuffer();
System.out.print("Append methods: ");
while (m.find()) {
m.appendReplacement(sb, "favour");
}
m.appendTail(sb);
System.out.println(sb.toString()); 4.5列印比對的所有字元串
Pattern patt = Pattern.compile("[A-Za-z][a-z]+");
BufferedReader r = new BufferedReader(new InputStreamReader(System.in));
String line;
while ((line = r.readLine()) != null) {
Matcher m = patt.matcher(line);
while (m.find()) {
int start = m.start(0);
int end = m.end(0);
System.out.println(line.substring(start, end));
}
}
r.close(); 5.4直接使用分數而不是浮點數
double d1 = 0.666 * 5;
System.out.println(d1);
double d2 = 2/3 * 5;
System.out.println(d2);
double d3 = 2d/3d * 5;
System.out.println(d3);
double d4 = (2*5)/3d;
System.out.println(d4);
int i5 = 2*5/3;
System.out.println(i5); 5.7舍入浮點數
public static final double THRESHOLD = 0.54;
public static int round(double d) {
return (int)Math.floor(d + 1.0 - THRESHOLD);
}
public static void main(String[] argv) {
for (double d = 0.1; d<=1.0; d+=0.05) {
System.out.println("My way: " + d + "-> " + round(d));
System.out.println("Math way:" + d + "-> " + Math.round(d));
}
} 5.8格式化數字
public static final double data[] = {0, 1, 22d/7, 100.2345678};
public static void main(String[] av) {
NumberFormat form = NumberFormat.getInstance();
form.setMinimumIntegerDigits(3);
form.setMinimumFractionDigits(2);
form.setMaximumFractionDigits(4);
for (int i=0; i<data.length; i++)
System.out.println(data[i] + "\tformats as " +
form.format(data[i]));
} 5.9二進制、八進制、十進制、十六進制之間轉換
String input = "101010";
for (int radix : new int[] { 2, 8, 10, 16, 36 }) {
System.out.print(input + " in base " + radix + " is "
+ Integer.valueOf(input, radix) + "; ");
int i = 42;
System.out.println(i + " formatted in base " + radix + " is "
+ Integer.toString(i, radix));
} 5.12複數的正确格式化
public static void main(String[] argv) {
report(0);
report(1);
report(2);
}
public static void report(int n) {
System.out.println("We used " + n + " item" + (n == 1 ? "" : "s"));
} 5.18處理非常大的數字
public static Object[] testInput = {
new BigDecimal("3419229223372036854775807.23343"),
new BigDecimal("2.0"),
"*",
};
public static void main(String[] args) {
BigNumCalc calc = new BigNumCalc();
System.out.println(calc.calculate(testInput));
}
Stack<BigDecimal> stack = new Stack<>();
public BigDecimal calculate(Object[] input) {
BigDecimal tmp;
for (int i = 0; i < input.length; i++) {
Object o = input[i];
if (o instanceof BigDecimal) {
stack.push((BigDecimal) o);
} else if (o instanceof String) {
switch (((String)o).charAt(0)) {
case '+':
stack.push((stack.pop()).add(stack.pop()));
break;
case '*':
stack.push((stack.pop()).multiply(stack.pop()));
break;
case '-':
tmp = (BigDecimal)stack.pop();
stack.push((stack.pop()).subtract(tmp));
break;
case '/':
tmp = stack.pop();
stack.push((stack.pop()).divide(tmp,
BigDecimal.ROUND_HALF_UP));
break;
default:
throw new IllegalStateException("Unknown OPERATOR popped");
}
} else {
throw new IllegalArgumentException("Syntax error in input");
}
}
return stack.pop();
} 5.19TempConverter
public static void main(String[] args) {
TempConverter t = new TempConverter();
t.start();
t.data();
t.end();
}
public void data() {
for (int i=-40; i<=120; i+=10) {
double c = fToC(i);
print(i, c);
}
}
public static double cToF(double deg) {
return ( deg * 9 / 5) + 32;
}
public static double fToC(double deg) {
return ( deg - 32 ) * ( 5d / 9 );
}
public void print(double f, double c) {
System.out.println(f + " " + c);
}
public void print(float f, float c) {
System.out.printf("%6.2f %6.2f%n", f, c);
}
public void start() {
System.out.println("Fahr Centigrade");
}
public void end() {
System.out.println("-------------------");
} 5.20數字回文
public static boolean verbose = true;
public static void main(String[] argv) {
for (int i=0; i<argv.length; i++)
try {
long l = Long.parseLong(argv[i]);
if (l < 0) {
System.err.println(argv[i] + " -> TOO SMALL");
continue;
}
System.out.println(argv[i] + "->" + findPalindrome(l));
} catch (NumberFormatException e) {
System.err.println(argv[i] + "-> INVALID");
} catch (IllegalStateException e) {
System.err.println(argv[i] + "-> " + e);
}
}
static long findPalindrome(long num) {
if (num < 0)
throw new IllegalStateException("negative");
if (isPalindrome(num))
return num;
if (verbose)
System.out.println("Trying " + num);
return findPalindrome(num + reverseNumber(num));
}
protected static final int MAX_DIGITS = 19;
static long[] digits = new long[MAX_DIGITS];
static boolean isPalindrome(long num) {
if (num >= 0 && num <= 9)
return true;
int nDigits = 0;
while (num > 0) {
digits[nDigits++] = num % 10;
num /= 10;
}
for (int i=0; i<nDigits/2; i++)
if (digits[i] != digits[nDigits - i - 1])
return false;
return true;
}
static long reverseNumber(long num) {
int nDigits = 0;
while (num > 0) {
digits[nDigits++] = num % 10;
num /= 10;
}
long ret = 0;
for (int i=0; i<nDigits; i++) {
ret *= 10;
ret += digits[i];
}
return ret;
} 6.1檢視當天日期
LocalDate dNow = LocalDate.now();
System.out.println(dNow);
LocalTime tNow = LocalTime.now();
System.out.println(tNow);
LocalDateTime now = LocalDateTime.now();
System.out.println(now); 6.2日期和時間的格式化
DateTimeFormatter df = DateTimeFormatter.ofPattern("yyyy/LL/dd");
System.out.println(df.format(LocalDate.now()));
System.out.println(LocalDate.parse("2014/04/01", df));
DateTimeFormatter nTZ = DateTimeFormatter.ofPattern("d MMMM, yyyy h:mm a");
System.out.println(ZonedDateTime.now().format(nTZ)); 6.3日期/時間、YMDHMS和紀元秒之間的轉換
Instant epochSec = Instant.ofEpochSecond(1000000000L);
ZoneId zId = ZoneId.systemDefault();
ZonedDateTime then = ZonedDateTime.ofInstant(epochSec, zId);
System.out.println("The epoch was a billion seconds old on " + then);
long epochSecond = ZonedDateTime.now().toInstant().getEpochSecond();
System.out.println("Current epoch seconds = " + epochSecond);
LocalDateTime now = LocalDateTime.now();
ZonedDateTime there = now.atZone(ZoneId.of("Canada/Pacific"));
System.out.printf("When it's %s here, it's %s in Vancouver%n",now, there); 6.4将字元串解析為日期
String armisticeDate = "1914-11-11";
LocalDate aLD = LocalDate.parse(armisticeDate);
System.out.println("Date: " + aLD);
String armisticeDateTime = "1914-11-11T11:11";
LocalDateTime aLDT = LocalDateTime.parse(armisticeDateTime);
System.out.println("Date/Time: " + aLDT);
//這裡好像有點問題
DateTimeFormatter df = DateTimeFormatter.ofPattern("dd MMM uuuu");
String anotherDate = "27 Jan 2012";
LocalDate random = LocalDate.parse(anotherDate, df);
System.out.println(anotherDate + " parses as " + random);
System.out.println(aLD + " formats as " + df.format(aLD)); 6.5兩個日期之間的差
LocalDate endofCentury = LocalDate.of(2000, 12, 31);
LocalDate now = LocalDate.now();
Period diff = Period.between(endofCentury, now);
System.out.printf("The 21st century (up to %s) is %s old%n", now, diff);
System.out.printf("The 21st century is %d years, %d months and %d days old",
diff.getYears(), diff.getMonths(), diff.getDays()); 6.6日期或月曆的加減
LocalDate now = LocalDate.now();
Period p = Period.ofDays(700);
LocalDate then = now.plus(p);
System.out.printf("Seven hundred days from %s is %s%n", now, then); 6.7與傳統日期和月曆類的接口
Date legacyDate = new Date();
System.out.println(legacyDate);
LocalDateTime newDate = LocalDateTime.ofInstant(legacyDate.toInstant(), ZoneId.systemDefault());
System.out.println(newDate);
Calendar c = Calendar.getInstance();
System.out.println(c);
LocalDateTime newCal = LocalDateTime.ofInstant(c.toInstant(),ZoneId.systemDefault());
System.out.println(newCal); 參考文獻
《Java經典執行個體》 lan F.Darwin著 李新葉 餘曉晔譯
轉載于:https://my.oschina.net/MoreYoungGavin/blog/906930
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