String common method analysis

1. LastIndexOf(String str) method analysis

 /**
     * Returns the index within this string of the last occurrence of the
     * specified substring.  The last occurrence of the empty string ""
     * is considered to occur at the index value {@code this.length()}.
     *
     * <p>The returned index is the largest value <i>k</i> for which:
     * <blockquote><pre>
     * this.startsWith(str, <i>k</i>)
     * </pre></blockquote>
     * If no such value of <i>k</i> exists, then {@code -1} is returned.
     *
     * @param   str   the substring to search for.要搜索的字符串
     * @return  the index of the last occurrence of the specified substring,
     *          or {@code -1} if there is no such occurrence.
     * Returns the position of the last occurrence of the string
     */
public int lastIndexOf(String str)

For example:

public static void main(String[] args) { 
        String string = "张三.txt"; 
        int length = string.length(); 
        System.out.println("The length of string is:" + length); 
        int lastIndexOf = string.lastIndexOf("."); 
        System.out.println("In string. The last subscript that appears is: "+ lastIndexOf); 
} The 

output result is: 

The length of 
string is: 6 in string. The last subscript that appears Yes: 2

 

2. Analysis of substring(int beginIndex) method

This method is often used in conjunction with the lastIndexOf(String str) method

 /**
     * Returns a string that is a substring of this string. The
     * substring begins with the character at the specified index and
     * extends to the end of this string. <p>
     * Examples:
     * <blockquote><pre>
     * "unhappy".substring(2) returns "happy"
     * "Harbison".substring(3) returns "bison"
     * "emptiness".substring(9) returns "" (an empty string)
     * </pre></blockquote>
     *
     * @param      beginIndex   the beginning index, inclusive. 截取的开始下标（包括开始下标）
     * @return     the specified substring. Returns all strings after the start index (including the start index) is intercepted  
     * @exception IndexOutOfBoundsException if
     * {@code beginIndex} is negative or larger than the
     *             length of this {@code String} object.
     */
    public String substring(int beginIndex)

Example: Get the suffix of a file

public static void main(String[] args) { 
        String string = "张三.txt"; 
        String suffix = string.substring((string.lastIndexOf(".")) + 1); 
        System.out.println("File The suffix is: "+ suffix); 
 } The 

output result is: the 
file suffix is: txt

 

3. Analysis of substring(int beginIndex, int endIndex) method

    /**
     * Returns a string that is a substring of this string. The
     * substring begins at the specified {@code beginIndex} and
     * extends to the character at index {@code endIndex - 1}.
     * Thus the length of the substring is {@code endIndex-beginIndex}.
     * <p>
     * Examples:
     * <blockquote><pre>
     * "hamburger".substring(4, 8) returns "urge"
     * "smiles".substring(1, 5) returns "mile"
     * </pre></blockquote>
     *
     * @param      beginIndex   the beginning index, inclusive. 开始下标（包括）
     * @param      endIndex     the ending index, exclusive. End subscript (not included) 
     * @return the specified substring.
     * @exception IndexOutOfBoundsException if the
     *             {@code beginIndex} is negative, or
     *             {@code endIndex} is larger than the length of
     *             this {@code String} object, or
     *             {@code beginIndex} is larger than
     *             {@code endIndex}.
     */
    public String substring(int beginIndex, int endIndex) 

 

Example: Get the file name of the file

  public static void main(String[] args) { 
        String string = "张三.txt"; 
        //Does not include lastIndexOf subscript 
        String name = string.substring(0, string.lastIndexOf(".")); 
        System.out .println("The file name is:" + name); 
}The 

output result is: the 
file name is: Zhang San