Here you can find the source of leftPad(String str, int size)
Left pad a String with spaces (' ').
| Parameter | Description |
|---|---|
| str | the String to pad out, may be null |
| size | the size to pad to |
null if null String input
public static String leftPad(String str, int size)
//package com.java2s; /******************************************************************************* * Copyright (c) 2011 MadRobot.//from w w w . ja v a 2 s. co m * All rights reserved. This program and the accompanying materials * are made available under the terms of the GNU Lesser Public License v2.1 * which accompanies this distribution, and is available at * http://www.gnu.org/licenses/old-licenses/gpl-2.0.html * * Contributors: * Elton Kent - initial API and implementation ******************************************************************************/ public class Main { /** * <p> * The maximum size to which the padding constant(s) can expand. * </p> */ private static final int PAD_LIMIT = 8192; /** * <p> * Left pad a String with spaces (' '). * </p> * * <p> * The String is padded to the size of <code>size</code>. * </p> * * <pre> * StringUtils.leftPad(null, *) = null * StringUtils.leftPad("", 3) = " " * StringUtils.leftPad("bat", 3) = "bat" * StringUtils.leftPad("bat", 5) = " bat" * StringUtils.leftPad("bat", 1) = "bat" * StringUtils.leftPad("bat", -1) = "bat" * </pre> * * @param str * the String to pad out, may be null * @param size * the size to pad to * @return left padded String or original String if no padding is necessary, * <code>null</code> if null String input */ public static String leftPad(String str, int size) { return leftPad(str, size, ' '); } /** * <p> * Left pad a String with a specified character. * </p> * * <p> * Pad to a size of <code>size</code>. * </p> * * <pre> * StringUtils.leftPad(null, *, *) = null * StringUtils.leftPad("", 3, 'z') = "zzz" * StringUtils.leftPad("bat", 3, 'z') = "bat" * StringUtils.leftPad("bat", 5, 'z') = "zzbat" * StringUtils.leftPad("bat", 1, 'z') = "bat" * StringUtils.leftPad("bat", -1, 'z') = "bat" * </pre> * * @param str * the String to pad out, may be null * @param size * the size to pad to * @param padChar * the character to pad with * @return left padded String or original String if no padding is necessary, * <code>null</code> if null String input */ public static String leftPad(String str, int size, char padChar) { if (str == null) { return null; } int pads = size - str.length(); if (pads <= 0) { return str; // returns original String when possible } if (pads > PAD_LIMIT) { return leftPad(str, size, String.valueOf(padChar)); } return padding(pads, padChar).concat(str); } /** * <p> * Left pad a String with a specified String. * </p> * * <p> * Pad to a size of <code>size</code>. * </p> * * <pre> * StringUtils.leftPad(null, *, *) = null * StringUtils.leftPad("", 3, "z") = "zzz" * StringUtils.leftPad("bat", 3, "yz") = "bat" * StringUtils.leftPad("bat", 5, "yz") = "yzbat" * StringUtils.leftPad("bat", 8, "yz") = "yzyzybat" * StringUtils.leftPad("bat", 1, "yz") = "bat" * StringUtils.leftPad("bat", -1, "yz") = "bat" * StringUtils.leftPad("bat", 5, null) = " bat" * StringUtils.leftPad("bat", 5, "") = " bat" * </pre> * * @param str * the String to pad out, may be null * @param size * the size to pad to * @param padStr * the String to pad with, null or empty treated as single space * @return left padded String or original String if no padding is necessary, * <code>null</code> if null String input */ public static String leftPad(String str, int size, String padStr) { if (str == null) { return null; } if (isBlank(padStr)) { padStr = " "; } int padLen = padStr.length(); int strLen = str.length(); int pads = size - strLen; if (pads <= 0) { return str; // returns original String when possible } if (padLen == 1 && pads <= PAD_LIMIT) { return leftPad(str, size, padStr.charAt(0)); } if (pads == padLen) { return padStr.concat(str); } else if (pads < padLen) { return padStr.substring(0, pads).concat(str); } else { char[] padding = new char[pads]; char[] padChars = padStr.toCharArray(); for (int i = 0; i < pads; i++) { padding[i] = padChars[i % padLen]; } return new String(padding).concat(str); } } /** * Gets a CharSequence length or <code>0</code> if the CharSequence is * <code>null</code>. * * @param cs * a CharSequence or <code>null</code> * @return CharSequence length or <code>0</code> if the CharSequence is * <code>null</code>. */ public static int length(CharSequence cs) { return cs == null ? 0 : cs.length(); } /** * <p> * Returns padding using the specified delimiter repeated to a given length. * </p> * * <pre> * StringUtils.padding(0, 'e') = "" * StringUtils.padding(3, 'e') = "eee" * StringUtils.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 < 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); } /** * <p> * Checks if a CharSequence is whitespace, empty ("") or null. * </p> * * <pre> * StringUtils.isBlank(null) = true * StringUtils.isBlank("") = true * StringUtils.isBlank(" ") = true * StringUtils.isBlank("bob") = false * StringUtils.isBlank(" bob ") = false * </pre> * * @param cs * the CharSequence to check, may be null * @return <code>true</code> if the CharSequence is null, empty or * whitespace */ public static boolean isBlank(CharSequence cs) { int strLen; if (cs == null || (strLen = cs.length()) == 0) { return true; } for (int i = 0; i < strLen; i++) { if ((Character.isWhitespace(cs.charAt(i)) == false)) { return false; } } return true; } }