java.lang.String类解析

成员变量

/**
 * 底层由数组存数据
 */
private final char value[];

/**
 * hash值
 */
private int hash;

方法

charAt

 /**
  * 返回指定下标的字符
  */
public char charAt(int index) {
     if ((index < 0) || (index >= value.length)) {
         throw new StringIndexOutOfBoundsException(index);
     }
     return value[index];
 }

compareTo、compareToIgnoreCase

  /**
   * 比较两个字符串的字典顺序，anotherString在后面的话就返回负数，相等为0，前面就正数
   */
public int compareTo(String anotherString) {
      int len1 = value.length;
      int len2 = anotherString.value.length;
      int lim = Math.min(len1, len2);
      char v1[] = value;
      char v2[] = anotherString.value;

      int k = 0;
      while (k < lim) {
          char c1 = v1[k];
          char c2 = v2[k];
          if (c1 != c2) {
              return c1 - c2;
          }
          k++;
      }
      return len1 - len2;
  }
  /**
   * 忽略大小写的对比
   */
  public int compareToIgnoreCase(String str) {
      return CASE_INSENSITIVE_ORDER.compare(this, str);
  }

concat

/**
 * 将指定的字符串参数连接到字符串上
 */
public String concat(String str) {
    int otherLen = str.length();
    if (otherLen == 0) {
        return this;
    }
    int len = value.length;
    char buf[] = Arrays.copyOf(value, len + otherLen);
    str.getChars(buf, len);
    return new String(buf, true);
}

contains

 /**
  * 是否存在此字符
  */
public boolean contains(CharSequence s) {
     return indexOf(s.toString()) > -1;
 }

contentEquals

  /**
   * 比较两者的内容是否相同，不检查被比较对象的类型
   */
public boolean contentEquals(CharSequence cs) {
      // Argument is a StringBuffer, StringBuilder
      if (cs instanceof AbstractStringBuilder) {
          if (cs instanceof StringBuffer) {
              synchronized(cs) {
                 return nonSyncContentEquals((AbstractStringBuilder)cs);
              }
          } else {
              return nonSyncContentEquals((AbstractStringBuilder)cs);
          }
      }
      // Argument is a String
      if (cs instanceof String) {
          return equals(cs);
      }
      // Argument is a generic CharSequence
      char v1[] = value;
      int n = v1.length;
      if (n != cs.length()) {
          return false;
      }
      for (int i = 0; i < n; i++) {
          if (v1[i] != cs.charAt(i)) {
              return false;
          }
      }
      return true;
  }
  /**
   * 还可以直接传入StringBuffer对比
   */
  public boolean contentEquals(StringBuffer sb) {
      return contentEquals((CharSequence)sb);
  }

copyValueOf

/**
 * 根据char数组new一个新的string
 */
public static String copyValueOf(char data[]) {
    return new String(data);
}
 /**
 * 更多参数new一个新的string
 */
public static String copyValueOf(char data[], int offset, int count) {
    return new String(data, offset, count);
}

endsWith、startsWith

/**
 * 比较是否与尾部的字符串一致
 */
public boolean endsWith(String suffix) {
    return startsWith(suffix, value.length - suffix.value.length);
}

/**
 * 对比指定范围的字符串是否一致
 */
public boolean startsWith(String prefix, int toffset) {
    char ta[] = value;
    int to = toffset;
    char pa[] = prefix.value;
    int po = 0;
    int pc = prefix.value.length;
    // Note: toffset might be near -1>>>1.
    if ((toffset < 0) || (toffset > value.length - pc)) {
        return false;
    }
    while (--pc >= 0) {
        if (ta[to++] != pa[po++]) {
            return false;
        }
    }
    return true;
}
    
/**
 * 比较是否与头部的字符串一致
 */
 public boolean startsWith(String prefix) {
    return startsWith(prefix, 0);
}

equals

  /**
   * 比较两者的内容是否相同，还会检查被比较对象的类型
   */
public boolean equals(Object anObject) {
      if (this == anObject) {
          return true;
      }
      if (anObject instanceof String) {
          String anotherString = (String)anObject;
          int n = value.length;
          if (n == anotherString.value.length) {
              char v1[] = value;
              char v2[] = anotherString.value;
              int i = 0;
              while (n-- != 0) {
                  if (v1[i] != v2[i])
                      return false;
                  i++;
              }
              return true;
          }
      }
      return false;
  }

format

/**
 * 字符串格式化
 * %s 字符串类型、 %c 字符类型、 %b 布尔类型、%d 整数类型（十进制）、%f 浮点类型.....
 */
public static String format(String format, Object... args) {
    return new Formatter().format(format, args).toString();
}

getBytes

 /**
  * char数组转换成byte 数组
  */
public byte[] getBytes() {
     return StringCoding.encode(value, 0, value.length);
 }

indexOf、lastIndexOf

 /**
  * 其实有很多重载方法，这是最常用的，返回第一次出现该字符串的下标，不存在返回-1
  */
public int indexOf(String str) {
     return indexOf(str, 0);
 }
 /**
  * 返回最后一次出现该字符串的下标，不存在返回-1
  */
 public int lastIndexOf(String str) {
     return lastIndexOf(str, value.length);
 }

length

/**
 * 经常会提问的数组跟String是属性还是方法
 */
public int length() {
    return value.length;
}

matches

/**
 * 检测字符串是否匹配给定的正则表达式
 */
    public boolean matches(String regex) {
    return Pattern.matches(regex, this);
}

replaceAll

/**
 * 替换指定字符串的内容
 */
public String replaceAll(String regex, String replacement) {
    return Pattern.compile(regex).matcher(this).replaceAll(replacement);
}

split

/**
 * 转换成数组，regex为区分标识
 */
public String[] split(String regex) {
    return split(regex, 0);
}

substring

/**
 * 从指定下标开始截取字符串
 * 感觉直接返回substring(beginIndex, value.length - beginIndex)可以吧
 */
    public String substring(int beginIndex) {
    if (beginIndex < 0) {
        throw new StringIndexOutOfBoundsException(beginIndex);
    }
    int subLen = value.length - beginIndex;
    if (subLen < 0) {
        throw new StringIndexOutOfBoundsException(subLen);
    }
    return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
}

/**
 * 从指定下标开始截取字符串
 */
 public String substring(int beginIndex, int endIndex) {
    if (beginIndex < 0) {
        throw new StringIndexOutOfBoundsException(beginIndex);
    }
    if (endIndex > value.length) {
        throw new StringIndexOutOfBoundsException(endIndex);
    }
    int subLen = endIndex - beginIndex;
    if (subLen < 0) {
        throw new StringIndexOutOfBoundsException(subLen);
    }
    return ((beginIndex == 0) && (endIndex == value.length)) ? this
            : new String(value, beginIndex, subLen);
}

toCharArray

/**
 * 转换成字符数组
 */
public char[] toCharArray() {
    // Cannot use Arrays.copyOf because of class initialization order issues
    char result[] = new char[value.length];
    System.arraycopy(value, 0, result, 0, value.length);
    return result;
}

toLowerCase、toUpperCase

/**
 * 全部转换小写
 */
 public String toLowerCase() {
    return toLowerCase(Locale.getDefault());
}
 /**
 * 全部转换大写
 */
public String toUpperCase() {
    return toUpperCase(Locale.getDefault());
}

valueOf

 /**
  * 转换成z
  */
 public static String valueOf(boolean b) {
     return b ? "true" : "false";
 }
 public static String valueOf(char data[]) {
     return new String(data);
 }
 public static String valueOf(char c) {
     char data[] = {c};
     return new String(data, true);
 }
 public static String valueOf(char data[], int offset, int count) {
     return new String(data, offset, count);
 }
 public static String valueOf(double d) {
     return Double.toString(d);
 }
 
public static String valueOf(float f) {
     return Float.toString(f);
 }
 public static String valueOf(int i) {
     return Integer.toString(i);
 }
 
 public static String valueOf(long l) {
     return Long.toString(l);
 }
 public static String valueOf(Object obj) {
     return (obj == null) ? "null" : obj.toString();
 }