Guava Strings 源碼分析

Strings

Stirngs是Guava對字符串操作提供的一些支持。

// 將null轉爲空字符串，不爲null返回源字符串
public static String nullToEmpty(@Nullable String string) {
    return (string == null) ? "" : string;
}

// 將空字符串轉爲null，不爲空返回源字符串
@Nullable
public static String emptyToNull(@Nullable String string) {
    return isNullOrEmpty(string) ? null : string;
}

// 判斷字符串是null或者空
public static boolean isNullOrEmpty(@Nullable String string) {
    return Platform.stringIsNullOrEmpty(string);
}

// 對於給定的string，如果長度小於minLength，在string首部填充padChar
public static String padStart(String string, int minLength, char padChar) {
    checkNotNull(string); // eager for GWT.
    if (string.length() >= minLength) {
      return string;
    }
    StringBuilder sb = new StringBuilder(minLength);
    for (int i = string.length(); i < minLength; i++) {
      sb.append(padChar);
    }
    // 首部填充
    sb.append(string);
    return sb.toString();
}

// 對於給定的string，如果長度小於minLength，在string尾部填充padChar
public static String padEnd(String string, int minLength, char padChar) {
    checkNotNull(string); // eager for GWT.
    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();
}

// 將string重複count倍返回
public static String repeat(String string, int count) {
    checkNotNull(string); // eager for GWT.
	
    if (count <= 1) {
    	// count >= 0 不成立，拋出IllegalArgumentException
        checkArgument(count >= 0, "invalid count: %s", count);
        // count=0，返回空，count=1，返回源字符串
        return (count == 0) ? "" : string;
    }

    // IF YOU MODIFY THE CODE HERE, you must update StringsRepeatBenchmark
    final int len = string.length();
    // 將repeat之後的長度len*count轉爲long類型
    final long longSize = (long) len * (long) count;
    
    // 判斷repeat之後的長度爲int類型時會不會發生截斷
    final int size = (int) longSize;
    if (size != longSize) {
        throw new ArrayIndexOutOfBoundsException("Required array size too large: " + longSize);
    }

	// 複製，使用char數組進行字符串裝載
    final char[] array = new char[size];
    string.getChars(0, len, array, 0);
    int n;
    // 使用
    for (n = len; n < size - n; n <<= 1) {
      System.arraycopy(array, 0, array, n, n);
    }
    System.arraycopy(array, 0, array, n, size - n);
    return new String(array);
}

// 返回公共最長前綴，無公共前綴返回空字符串
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();
}

// 返回公共最長後綴，無公共後綴返回空字符串
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();
}