Repeat a String repeat times to form a new String. - Java java.lang

Java examples for java.lang:String New Line

  1. HOME
  2. Java
  3. java.lang
  4. String New Line

Description

Repeat a String repeat times to form a new String.

Demo Code

/*//from  ww  w. j  av  a  2s  .co  m
 * Copyright 2013 Guidewire Software, Inc.
 */
/**
 * This class is based, in part, on org.apache.commons.lang.StringUtils and is intended
 * to break the dependency on that project.
 *
 * @author <a href="http://jakarta.apache.org/turbine/">Apache Jakarta Turbine</a>
 * @author <a href="mailto:jon@latchkey.com">Jon S. Stevens</a>
 * @author Daniel L. Rall
 * @author <a href="mailto:gcoladonato@yahoo.com">Greg Coladonato</a>
 * @author <a href="mailto:ed@apache.org">Ed Korthof</a>
 * @author <a href="mailto:rand_mcneely@yahoo.com">Rand McNeely</a>
 * @author Stephen Colebourne
 * @author <a href="mailto:fredrik@westermarck.com">Fredrik Westermarck</a>
 * @author Holger Krauth
 * @author <a href="mailto:alex@purpletech.com">Alexander Day Chaffee</a>
 * @author <a href="mailto:hps@intermeta.de">Henning P. Schmiedehausen</a>
 * @author Arun Mammen Thomas
 * @author Gary Gregory
 * @author Phil Steitz
 * @author Al Chou
 * @author Michael Davey
 * @author Reuben Sivan
 * @author Chris Hyzer
 *  Johnson

 */
//package com.java2s;

public class Main {
    public static void main(String[] argv) {
        String str = "java2s.com";
        int repeat = 42;
        System.out.println(repeat(str, repeat));
    }

    /**
     * The empty String <code>""</code>.
     * @since 2.0
     */
    public static final String EMPTY = "";
    /**
     * <p>The maximum size to which the padding constant(s) can expand.</p>
     */
    private static final int PAD_LIMIT = 8192;

    /**
     * <p>Repeat a String <code>repeat</code> times to form a
     * new String.</p>
     *
     * <pre>
     * repeat(null, 2) = null
     * repeat("", 0)   = ""
     * repeat("", 2)   = ""
     * repeat("a", 3)  = "aaa"
     * repeat("ab", 2) = "abab"
     * repeat("a", -2) = ""
     * </pre>
     *
     * @param str  the String to repeat, may be null
     * @param repeat  number of times to repeat str, negative treated as zero
     * @return a new String consisting of the original String repeated,
     *  <code>null</code> if null String input
     */
    public static String repeat(String str, int repeat) {
        // Performance tuned for 2.0 (JDK1.4)

        if (str == null) {
            return null;
        }
        if (repeat <= 0) {
            return EMPTY;
        }
        int inputLength = str.length();
        if (repeat == 1 || inputLength == 0) {
            return str;
        }
        if (inputLength == 1 && repeat <= PAD_LIMIT) {
            return padding(repeat, str.charAt(0));
        }

        int outputLength = inputLength * repeat;
        switch (inputLength) {
        case 1:
            char ch = str.charAt(0);
            char[] output1 = new char[outputLength];
            for (int i = repeat - 1; i >= 0; i--) {
                output1[i] = ch;
            }
            return new String(output1);
        case 2:
            char ch0 = str.charAt(0);
            char ch1 = str.charAt(1);
            char[] output2 = new char[outputLength];
            for (int i = repeat * 2 - 2; i >= 0; i--, i--) {
                output2[i] = ch0;
                output2[i + 1] = ch1;
            }
            return new String(output2);
        default:
            StringBuilder buf = new StringBuilder(outputLength);
            for (int i = 0; i < repeat; i++) {
                buf.append(str);
            }
            return buf.toString();
        }
    }

    /**
     * Gets a String's length or <code>0</code> if the String is <code>null</code>.
     *
     * @param str
     *            a String or <code>null</code>
     * @return String length or <code>0</code> if the String is <code>null</code>.
     * @since 2.4
     */
    public static int length(String str) {
        return str == null ? 0 : str.length();
    }

    /**
     * <p>Returns padding using the specified delimiter repeated
     * to a given length.</p>
     *
     * <pre>
     * padding(0, 'e')  = ""
     * padding(3, 'e')  = "eee"
     * padding(-2, 'e') = IndexOutOfBoundsException
     * </pre>
     *
     * <p>Note: this method doesn't not support padding with
     * <a href="http://www.unicode.org/glossary/#supplementary_character">Unicode Supplementary Characters</a>
     * as they require a pair of <code>char</code>s to be represented.
     * If you are needing to support full I18N of your applications
     * consider using {@link #repeat(String, int)} instead.
     * </p>
     *
     * @param repeat  number of times to repeat delim
     * @param padChar  character to repeat
     * @return String with repeated character
     * @throws IndexOutOfBoundsException if <code>repeat &lt; 0</code>
     * @see #repeat(String, int)
     */
    private static String padding(int repeat, char padChar)
            throws IndexOutOfBoundsException {
        if (repeat < 0) {
            throw new IndexOutOfBoundsException(
                    "Cannot pad a negative amount: " + repeat);
        }
        final char[] buf = new char[repeat];
        for (int i = 0; i < buf.length; i++) {
            buf[i] = padChar;
        }
        return new String(buf);
    }
}

Related Tutorials