JAVA字符处理，java字符

JAVA字符处理，java字符

StringBuffer buf = new StringBuffer("Java");

    // Append

    buf.append(" Almanac v1/");      // Java Almanac v1/

    buf.append(3);                   // Java Almanac v1/3

    // Set

    int index = 15;

    buf.setCharAt(index, '.');       // Java Almanac v1.3

    // Insert

    index = 5;

    buf.insert(index, "Developers ");// Java Developers Almanac v1.3

    // Replace

    int start = 27;

    int end = 28;

    buf.replace(start, end, "4");    // Java Developers Almanac v1.4

    // Delete

    start = 24;

    end = 25;

    buf.delete(start, end);          // Java Developers Almanac 1.4

    // Convert to string

    String s = buf.toString();

比较字符串

String s1 = "a";

    String s2 = "A";

    String s3 = "B";

    // Check if identical 监测是否一致

    boolean b = s1.equals(s2);           // false

    // Check if identical ignoring case

    b = s1.equalsIgnoreCase(s2);         // true

    // Check order of two strings 监测两个字符串的顺序

    int i = s1.compareTo(s2);            // 32; lowercase follows uppercase

    if (i < 0) {

        // s1 precedes s2

    } else if (i > 0) {

        // s1 follows s2

    } else {

        // s1 equals s2

    }

    // Check order of two strings ignoring case

    i = s1.compareToIgnoreCase(s3);      // -1

    if (i < 0) {

        // s1 precedes s3

    } else if (i > 0) {

        // s1 follows s3

    } else {

        // s1 equals s3

    }

    // A string can also be compared with a StringBuffer;

    StringBuffer sbuf = new StringBuffer("a");

    b = s1.contentEquals(sbuf);          // true

判断一个字符串中是否包含另外一个字符串

String string = "Madam, I am Adam";

    // Starts with

    boolean b = string.startsWith("Mad"); // true

    // Ends with

    b = string.endsWith("dam");             // true

    // Anywhere

    b = string.indexOf("I am") > 0;         // true

    // To ignore case, regular expressions must be used

    // Starts with

    b = string.matches("(?i)mad.*");

    // Ends with

    b = string.matches("(?i).*adam");

    // Anywhere

    b = string.matches("(?i).*i am.*");

获取制定字符串中的子串

int start = 1;

    int end = 4;

    String substr = "aString".substring(start, end);  // Str

查询指定字符串中的子串以及字母的位置

String string = "madam, i am Adam";

    // Characters

        // First occurrence of a c

        int index = string.indexOf('a');    // 1

        // Last occurrence

        index = string.lastIndexOf('a');    // 14

        // Not found

        index = string.lastIndexOf('z');    // -1

    // Substrings

        // First occurrence

        index = string.indexOf("dam");      // 1

        // Last occurrence

        index = string.lastIndexOf("dam"); // 13

        // Not found

        index = string.lastIndexOf("z");    // -1

取代制定字符的函数操作

// Replace all occurrences of 'a' with 'o'

    String newString = string.replace('a', 'o');

取代制定字符串的操作

static String replace(String str, String pattern, String replace) {

        int s = 0;

        int e = 0;

        StringBuffer result = new StringBuffer();

        while ((e = str.indexOf(pattern, s)) >= 0) {

            result.append(str.substring(s, e));

            result.append(replace);

            s = e+pattern.length();

        }

        result.append(str.substring(s));

        return result.toString();

    }

转变字符串的大小写

// Convert to upper case

    String upper = string.toUpperCase();

    // Convert to lower case

    String lower = string.toLowerCase();

Converting a Primitive Type Value to a String

// Use String.valueOf()

    String s = String.valueOf(true);     // true

    s = String.valueOf((byte)0x12);      // 18

    s = String.valueOf((byte)0xFF);      // -1

    s = String.valueOf('a');             // a

    s = String.valueOf((short)123);      // 123

    s = String.valueOf(123);             // 123

    s = String.valueOf(123L);            // 123

    s = String.valueOf(1.23F);           // 1.23

    s = String.valueOf(1.23D);           // 1.23

    // Use +

    s = ""+true;                         // true

    s = ""+((byte)0x12);                 // 18

   s = ""+((byte)0xFF);                 // -1

    s = ""+'a';                          // a

    s = ""+((short)123);                 // 123

    s = ""+123;                          // 123

    s = ""+123L;                         // 123

    s = ""+1.23F;                        // 1.23

    s = ""+1.23D;                        // 1.23

Converting Between Unicode and UTF-8

try {

        // Convert from Unicode to UTF-8

        String string = "abc/u5639/u563b";

        byte[] utf8 = string.getBytes("UTF-8");

        // Convert from UTF-8 to Unicode

        string = new String(utf8, "UTF-8");

    } catch (UnsupportedEncodingException e) {

    }

Determining a Character's Unicode Block

char ch = '/u5639';

    Character.UnicodeBlock block = Character.UnicodeBlock.of(ch);

Determining If a String Is a Legal Java Identifier

// Returns true if s is a legal Java identifier.

    public static boolean isJavaIdentifier(String s) {

        if (s.length() == 0 || !Character.isJavaIdentifierStart(s.charAt(0))) {

            return false;

        }

        for (int i=1; i<s.length(); i++) {

            if (!Character.isJavaIdentifierPart(s.charAt(i))) {

                return false;

            }

        }

        return true;

    }

    // Some examples

    boolean b = isJavaIdentifier("my_var"); // true

    b = isJavaIdentifier("my_var.1");       // false

    b = isJavaIdentifier("$my_var");        // true

    b = isJavaIdentifier("/u0391var");      // true

    b = isJavaIdentifier("_");              // true

    b = isJavaIdentifier("___FCKpd___175quot;);              // true

    b = isJavaIdentifier("1$my_var");       // false

Numbers 精确计算类实例 package hxj; import java.math.BigDecimal; /** * 由于Java的简单类型不能够精确的对浮点数进行运算，这个工具类提供精 * 确的浮点数运算，包括加减乘除和四舍五入。 */ public class mymatch { //默认除法运算精度 private static final int DEF_DIV_SCALE = 10; //这个类不能实例化 private Arith() {} /** * 提供精确的加法运算。 * @param v1 被加数 * @param v2 加数 * @return 两个参数的和 */ public static double add(double v1, double v2) { BigDecimal b1 = new BigDecimal(Double.toString(v1)); BigDecimal b2 = new BigDecimal(Double.toString(v2)); return b1.add(b2).doubleValue(); } /** * 提供精确的减法运算。 * @param v1 被减数 * @param v2 减数 * @return 两个参数的差 */ public static double sub(double v1, double v2) { BigDecimal b1 = new BigDecimal(Double.toString(v1)); BigDecimal b2 = new BigDecimal(Double.toString(v2)); return b1.subtract(b2).doubleValue(); } /** * 提供精确的乘法运算。 * @param v1 被乘数 * @param v2 乘数 * @return 两个参数的 */ public static double mul(double v1, double v2) { BigDecimal b1 = new BigDecimal(Double.toString(v1)); BigDecimal b2 = new BigDecimal(Double.toString(v2)); return b1.multiply(b2).doubleValue(); } /** * 提供（相对）精确的除法运算，当发生除不尽的情况时，精确到 * 小数点以后10位，以后的数字四舍五入。 * @param v1 被除数 * @param v2 除数 * @return 两个参数的商 */ public static double div(double v1, double v2) { return div(v1, v2, DEF_DIV_SCALE); } /** * 提供（相对）精确的除法运算。当发生除不尽的情况时，由scale参数指 * 定精度，以后的数字四舍五入。 * @param v1 被除数 * @param v2 除数 * @param scale 表示表示需要精确到小数点以后几位。 * @return 两个参数的商 */ public static double div(double v1, double v2, int scale) { if (scale < 0) { throw new IllegalArgumentException("The scale must be a positive integer or zero"); } BigDecimal b1 = new BigDecimal(Double.toString(v1)); BigDecimal b2 = new BigDecimal(Double.toString(v2)); return b1.divide(b2, scale, BigDecimal.ROUND_HALF_UP).doubleValue(); } /** * 提供精确的小数位四舍五入处理。 * @param v 需要四舍五入的数字 * @param scale 小数点后保留几位 * @return 四舍五入后的结果 */ public static double round(double v, int scale) { if (scale < 0) { throw new IllegalArgumentException("The scale must be a positive integer or zero"); } BigDecimal b = new BigDecimal(Double.toString(v)); BigDecimal one = new BigDecimal("1"); return b.divide(one, scale, BigDecimal.ROUND_HALF_UP).doubleValue(); } }; 转变字符串为数字格式

byte b = Byte.parseByte("123");

    short s = Short.parseShort("123");

    int i = Integer.parseInt("123");

    long l = Long.parseLong("123");

    float f = Float.parseFloat("123.4");

    double d = Double.parseDouble("123.4e10");

Parsing and Formatting a Number into Binary, Octal, and Hexadecimal

 int i = 1023;

    // Parse and format to binary

    i = Integer.parseInt("1111111111", 2); // 1023

    String s = Integer.toString(i, 2);     // 1111111111

    // Parse and format to octal

    i = Integer.parseInt("1777", 8);       // 1023

    s = Integer.toString(i, 8);            // 1777

    // Parse and format to decimal

    i = Integer.parseInt("1023");          // 1023

    s = Integer.toString(i);               // 1023

    // Parse and format to hexadecimal

    i = Integer.parseInt("3ff", 16);       // 1023

    s = Integer.toString(i, 16);           // 3ff

    // Parse and format to arbitrary radix <= Character.MAX_RADIX

    int radix = 32;

    i = Integer.parseInt("vv", radix);     // 1023

    s = Integer.toString(i, radix);        // vv