Notas de um tecnólogo

String concat is something that we need to do a lot when creating SQLs but there is a problem by using string-plus-string concatenation (“string”+”"string”): Every couple of quotations java will create and alocate one String class, this can be a trigger for memory problems.

The orientation (at Celepar) is to use StringBuffer that is faster than simple concat. Searching the web i found that StringBuilder is a bit faster than StringBuffer.

Now let me go to the point, i needed to make an join and use a separator at a group of strings, but memory was something i was worried, then i tried to simulate an array over StringBuilder,  the result was the following class.

p.s: I really doen’t feel that there aren’t a better and faster way to do this, but i didn’t found anything at this time;

package com.br.webcentro.utils;

import java.util.Arrays;

/**
 * This class works using the java.lang.StringBuilder,
 * but this simulates an array to implement a joinable splitable string
 *
 * may be better extend the class AbstractStringBuilder but for now it will only work using it;
 *
 * feel free to post implementations
 *
 * If you have some advice please contact me at webcentro(at)gmail.com
 * @author alandanielweiss
 * @since 2010-01-22
 */

public class ArrayStringBuilder implements java.io.Serializable{

	private StringBuilder builder;

	private boolean isMultiEnabled = false;
	private boolean isEmptyAllowed = true;

	private int start[];
	private int len[];
	private int counter=0;
	private int totalLen=0;

	private static final long serialVersionUID = -2443226579329551214L;

	/**
     * Constructs a string builder with no characters in it and an
     * initial capacity of 16 characters.
     */

	public ArrayStringBuilder() {
		this.builder = new StringBuilder();
		this.start   = new int[16];
		this.len     = new int[16];
    }

	/**
	 * Sets the initial StringBuilder capacity
	 * @param capacity
	 */
	public ArrayStringBuilder(int capacity) {
		this.builder = new StringBuilder(capacity);
		this.start   = new int[capacity];
		this.len     = new int[capacity];
    }

	/**
	 * Create class and append string
	 * @param string
	 */
    public ArrayStringBuilder(String string) {
    	this();
    	this.add(string);
    }

	/**
	 * Create class and the the StringBuilder
	 * @param string
	 */
    public ArrayStringBuilder(StringBuilder builder) {
		this.start   = new int[16];
		this.len     = new int[16];

		this.counter = 1;
    	this.start[0] = 0;
    	this.len[0] = builder.toString().length();
    	this.totalLen = this.len[0];

    	this.builder = builder;
    }

    /**
     * Append a string
     * @param str
     * @return
     */
	public ArrayStringBuilder add(String str){
		if (str == null)
			str = "null";
	    int len = str.length();
		if (len == 0 && !isEmptyAllowed)
			return this;

		//multi-line don't increment counter
		if(!this.isMultiEnabled)
			this.counter ++;

		if (this.counter > start.length)
		    expandCapacity(this.counter);

		if(!this.isMultiEnabled)
			this.start[this.counter-1] = this.totalLen;

		if(this.isMultiEnabled)
			len +=this.len[this.counter-1];

		this.len[this.counter-1]   = len;

		this.totalLen += str.length();
		this.builder.append(str);
		return this;
	}

	/**
	 * start multiline array
	 * when done use the method end()
	 * @return
	 */
	public ArrayStringBuilder start(String str){
		this.isMultiEnabled = false;
		this.add(str);
		this.isMultiEnabled = true;
		return this;
	}

	/**
	 * finish multiline array
	 * @return
	 */
	public ArrayStringBuilder finish(String str){
		this.add(str);
		this.isMultiEnabled = false;
		return this;
	}

	void expandCapacity(int minimumCapacity) {
		int newCapacity = (start.length + 1) * 2;
        if (newCapacity < 0) {
        	newCapacity = Integer.MAX_VALUE;
        } else if (minimumCapacity > newCapacity) {
        	newCapacity = minimumCapacity;
		}
        this.start = Arrays.copyOf(this.start, newCapacity);
        this.len = Arrays.copyOf(this.len, newCapacity);
    }

	/**
	 * Joins the StringBuilder using the passed separator
	 * @param separator
	 * @return
	 */
	public String join(String separator){
		StringBuilder str = new StringBuilder();
		for (int idx=0; idx<this.counter;idx++){
			str.append(this.builder.substring(this.start[idx], this.start[idx]+this.len[idx]));
			if(idx+1<this.counter)
				str.append(separator);
	    }
		return str.toString();
	}

	public String[] toArray(){
		String[] str = new String[this.counter];
		for (int idx=0; idx<this.counter;idx++){
			str[idx] = this.builder.substring(this.start[idx], this.start[idx]+this.len[idx]);
	    }
		return str;
	}

	/**
	 * To string...
	 * @return String
	 */
    public String toString() {
    	return this.builder.toString();
    }

    /**
     * Creates a StringBuilder with the actual object values
     * @return builder:StringBuilder
     */
    public StringBuilder getStringBuilder(){
    	return this.builder;
    }

    /**
     * when true every time you use add/start/finish with an empty string it will add a new array
     * if false the command add/start/finish empty has no effect
     */
    public void setEmptyAllowed(boolean isMultiEnabled){
    	this.isMultiEnabled = isMultiEnabled;
    }

    public static void main(String[] args) {
		//Sample 1
    	StringBuilder strb = new StringBuilder();
    	strb.append("to be");
    	ArrayStringBuilder arrb = new ArrayStringBuilder(strb);
    	arrb.start(" or ");
    	arrb.add("not ");
    	arrb.add("to ");
    	arrb.finish("be");
		ArrayStringBuilder arrb2 = new ArrayStringBuilder(arrb.join(","));
		System.out.println(arrb2.add(": that's").add("the").add("question").join(" "));

		//Sample 2
		ArrayStringBuilder fields = new ArrayStringBuilder();
		fields.add("id");
		if(1==1)
			fields.add("name");
		if(1==2)
			fields.add("profession");
		StringBuilder sql = new StringBuilder();
		sql.append("select ").append(fields.join(" , ")).append(" from table ");
		System.out.println(sql.toString());
	}
}

A good comparision between StringBuilder and StringBuffer can be found at: StringBuilder vs StringBuffer vs String.concat – done right

Please feel free to send comments, to improve this class.