Tests if this string starts with the specified prefix. - Java java.lang

Java examples for java.lang:String Start

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Description

Tests if this string starts with the specified prefix.

Demo Code


//package com.java2s;

public class Main {
    public static void main(String[] argv) throws Exception {
        StringBuilder sb = new StringBuilder();
        String prefix = "java2s.com";
        System.out.println(startsWith(sb, prefix));
    }//  w w w.j a  v a 2  s  . co m

    /**
     * Tests if this string starts with the specified prefix.
     *
     * @param prefix the prefix.
     * @return  <code>true</code> if the character sequence represented by the
     *          argument is a prefix of the character sequence represented by
     *          this string; <code>false</code> otherwise.
     *          Note also that <code>true</code> will be returned if the
     *          argument is an empty string or is equal to this
     *          <code>StringBuilder</code> object as determined by 
     *          comparing the corresponding string obtained by
     *          calling the {@link StringBuilder#toString()} method.
     */
    public static boolean startsWith(StringBuilder sb, String prefix) {
        return startsWith(sb, prefix, 0);
    }

    /**
     * Tests if the substring of the specified <tt>StringBuilder</tt> 
     * beginning at the specified index starts with the specified prefix.
     *
     * @param sb
     * @param prefix the prefix.
     * @param offset where to begin looking in this string.
     * @return  <code>true</code> if the character sequence represented by the
     *          argument is a prefix of the substring of this object starting
     *          at index <code>offset</code>; <code>false</code> otherwise.
     *          The result is <code>false</code> if <code>toffset</code> is
     *          negative or greater than the length of this
     *          <code>StringBuilder</code> object; otherwise the result 
     *          is the same as the result of the expression
     *          <pre>
     *          sb.substring(offset).startsWith(prefix)
     *          </pre>
     */
    public static boolean startsWith(StringBuilder sb, String prefix,
            int offset) {
        if (offset < 0 || sb.length() - offset < prefix.length())
            return false;

        int len = prefix.length();
        for (int i = 0; i < len; ++i) {
            if (sb.charAt(offset + i) != prefix.charAt(i))
                return false;
        }
        return true;
    }
}

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