@GwtCompatible public final class Strings { private Strings() {} /** *若string为null,则返回空串;否则,返回自身 */ public static String nullToEmpty(@Nullable String string) { return (string == null) ? "" : string; } /** * 若string为null或者empty,都返回null;否则,返回自身 */ @Nullable public static String emptyToNull(@Nullable String string) { return isNullOrEmpty(string) ? null : string; } /** *当string为null或者为空时,返回true;否则,返回false *这里判断空串是通过length()==0,而java6中是isEmpty() */ public static boolean isNullOrEmpty(@Nullable String string) { return string == null || string.length() == 0; // string.isEmpty() in Java 6 } /** * 字符串填补 * @param string 放在结果字符串的最后一部分 * @param minLength 返回结果串应该具有的最小长度。可以为0或者负数,这样返回的是string本身 * @param padChar 用于填补的字符,插入在string的前面,插入次数直到返回串的总长度达到minLength * @return the padded string */ public static String padStart(String string, int minLength, char padChar) { checkNotNull(string); if (string.length() >= minLength) { return string; } StringBuilder sb = new StringBuilder(minLength); for (int i = string.length(); i < minLength; i++) { sb.append(padChar); } sb.append(string); return sb.toString(); } /** * 与padStart类似,只不过padChar放到了string的后面 */ public static String padEnd(String string, int minLength, char padChar) { checkNotNull(string); if (string.length() >= minLength) { return string; } StringBuilder sb = new StringBuilder(minLength); sb.append(string); for (int i = string.length(); i < minLength; i++) { sb.append(padChar); } return sb.toString(); } /** *字符串拷贝 * @param string 非空字符串 * @param count 重复次数,非负的 * @return a string containing {@code string} repeated {@code count} times * (the empty string if {@code count} is zero) * @throws IllegalArgumentException if {@code count} is negative */ public static String repeat(String string, int count) { checkNotNull(string); // eager for GWT. if (count <= 1) { checkArgument(count >= 0, "invalid count: %s", count); return (count == 0) ? "" : string; } final int len = string.length(); final long longSize = (long) len * (long) count; final int size = (int) longSize; //如果最后得到的字符串过长,直接抛出异常 if (size != longSize) { throw new ArrayIndexOutOfBoundsException( "Required array size too large: " + longSize); } final char[] array = new char[size]; //直接调用系统的字符串拷贝函数:System.arraycopy(value, srcBegin, dst, dstBegin, srcEnd - srcBegin); string.getChars(0, len, array, 0); int n; for (n = len; n < size - n; n <<= 1) { System.arraycopy(array, 0, array, n, n); } //最后一次拷贝,拷贝长度是size-n System.arraycopy(array, 0, array, n, size - n); return new String(array); } /** *计算两个字符串的公共前缀 */ public static String commonPrefix(CharSequence a, CharSequence b) { checkNotNull(a); checkNotNull(b); int maxPrefixLength = Math.min(a.length(), b.length()); int p = 0; while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) { p++; } if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) { p--; } return a.subSequence(0, p).toString(); } /** * 同commonPrefix,只不过求的是公共后缀 */ public static String commonSuffix(CharSequence a, CharSequence b) { checkNotNull(a); checkNotNull(b); int maxSuffixLength = Math.min(a.length(), b.length()); int s = 0; while (s < maxSuffixLength && a.charAt(a.length() - s - 1) == b.charAt(b.length() - s - 1)) { s++; } if (validSurrogatePairAt(a, a.length() - s - 1) || validSurrogatePairAt(b, b.length() - s - 1)) { s--; } return a.subSequence(a.length() - s, a.length()).toString(); } @VisibleForTesting static boolean validSurrogatePairAt(CharSequence string, int index) { return index >= 0 && index <= (string.length() - 2) && Character.isHighSurrogate(string.charAt(index)) && Character.isLowSurrogate(string.charAt(index + 1)); } }
时间: 2024-11-06 11:57:10