Gets the leftmost len characters of a String. If len characters are not available, or the String is null, the String will be returned without an exception. - Java java.lang

Java examples for java.lang:String Start

Description

Gets the leftmost len characters of a String. If len characters are not available, or the String is null, the String will be returned without an exception.

Demo Code

/*/*from  w  w  w  .j  av  a2s  .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 len = 42;
        System.out.println(left(str, len));
    }

    /**
     * The empty String <code>""</code>.
     * @since 2.0
     */
    public static final String EMPTY = "";

    /**
     * <p>Gets the leftmost <code>len</code> characters of a String.</p>
     *
     * <p>If <code>len</code> characters are not available, or the
     * String is <code>null</code>, the String will be returned without
     * an exception. An exception is thrown if len is negative.</p>
     *
     * <pre>
     * left(null, *)    = null
     * left(*, -ve)     = ""
     * left("", *)      = ""
     * left("abc", 0)   = ""
     * left("abc", 2)   = "ab"
     * left("abc", 4)   = "abc"
     * </pre>
     *
     * @param str  the String to get the leftmost characters from, may be null
     * @param len  the length of the required String, must be zero or positive
     * @return the leftmost characters, <code>null</code> if null String input
     */
    public static String left(String str, int len) {
        if (str == null) {
            return null;
        }
        if (len < 0) {
            return EMPTY;
        }
        if (str.length() <= len) {
            return str;
        }
        return str.substring(0, len);
    }

    /**
     * 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>Gets a substring from the specified String avoiding exceptions.</p>
     *
     * <p>A negative start position can be used to start <code>n</code>
     * characters from the end of the String.</p>
     *
     * <p>A <code>null</code> String will return <code>null</code>.
     * An empty ("") String will return "".</p>
     *
     * <pre>
     * substring(null, *)   = null
     * substring("", *)     = ""
     * substring("abc", 0)  = "abc"
     * substring("abc", 2)  = "c"
     * substring("abc", 4)  = ""
     * substring("abc", -2) = "bc"
     * substring("abc", -4) = "abc"
     * </pre>
     *
     * @param str  the String to get the substring from, may be null
     * @param start  the position to start from, negative means
     *  count back from the end of the String by this many characters
     * @return substring from start position, <code>null</code> if null String input
     */
    public static String substring(String str, int start) {
        if (str == null) {
            return null;
        }

        // handle negatives, which means last n characters
        if (start < 0) {
            start = str.length() + start; // remember start is negative
        }

        if (start < 0) {
            start = 0;
        }
        if (start > str.length()) {
            return EMPTY;
        }

        return str.substring(start);
    }

    /**
     * <p>Gets a substring from the specified String avoiding exceptions.</p>
     *
     * <p>A negative start position can be used to start/end <code>n</code>
     * characters from the end of the String.</p>
     *
     * <p>The returned substring starts with the character in the <code>start</code>
     * position and ends before the <code>end</code> position. All position counting is
     * zero-based -- i.e., to start at the beginning of the string use
     * <code>start = 0</code>. Negative start and end positions can be used to
     * specify offsets relative to the end of the String.</p>
     *
     * <p>If <code>start</code> is not strictly to the left of <code>end</code>, ""
     * is returned.</p>
     *
     * <pre>
     * substring(null, *, *)    = null
     * substring("", * ,  *)    = "";
     * substring("abc", 0, 2)   = "ab"
     * substring("abc", 2, 0)   = ""
     * substring("abc", 2, 4)   = "c"
     * substring("abc", 4, 6)   = ""
     * substring("abc", 2, 2)   = ""
     * substring("abc", -2, -1) = "b"
     * substring("abc", -4, 2)  = "ab"
     * </pre>
     *
     * @param str  the String to get the substring from, may be null
     * @param start  the position to start from, negative means
     *  count back from the end of the String by this many characters
     * @param end  the position to end at (exclusive), negative means
     *  count back from the end of the String by this many characters
     * @return substring from start position to end positon,
     *  <code>null</code> if null String input
     */
    public static String substring(String str, int start, int end) {
        if (str == null) {
            return null;
        }

        // handle negatives
        if (end < 0) {
            end = str.length() + end; // remember end is negative
        }
        if (start < 0) {
            start = str.length() + start; // remember start is negative
        }

        // check length next
        if (end > str.length()) {
            end = str.length();
        }

        // if start is greater than end, return ""
        if (start > end) {
            return EMPTY;
        }

        if (start < 0) {
            start = 0;
        }
        if (end < 0) {
            end = 0;
        }

        return str.substring(start, end);
    }
}

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