LDEV-2127 use stringbuilder for bytecode (v2)

[zspitzer]

refiled from #1758 as rebase got ugly)

https://luceeserver.atlassian.net/browse/LDEV-2127

code review comments still pending

[michaeloffner]

instead of calling append twice, call the constructor with a string, so instead of
new StringBuilder().append(left).append(right).toString();
you do
new StringBuilder(left).append(right).toString();

OR maybe the following is faster?
new StringBuilder(left.length()+right.length()).append(left).append(right).toString();

[michaeloffner]

i still think that StringBuilder comes with unnecessary overhead

[michaeloffner]

thinking about it, i think we can break down what StringBuilder makes and create a method that does the same but much more optimized

[michaeloffner]

created some test code

public static void main(String[] args) {
		int max = 1000000;
		double tmp, start, res1 = Double.MAX_VALUE, res2 = Double.MAX_VALUE, res3 = Double.MAX_VALUE, res4 = Double.MAX_VALUE;
		String left = "John Maynard war unser Steuermann, Aushielt er, bis er das Ufer gewann, ";
		String right = "Er hat uns gerettet, er trägt die Kron, Er starb für uns, unsre Liebe sein Lohn.";
		for (int y = 0; y < 100; y++) {

			// ()
			start = SystemUtil.millis();
			for (int i = 0; i < max; i++) {
				new StringBuilder().append(left).append(right).toString();
			}
			tmp = SystemUtil.millis() - start;
			if (tmp < res1) res1 = tmp;

			// (String)
			start = SystemUtil.millis();
			for (int i = 0; i < max; i++) {
				new StringBuilder(left).append(right).toString();
			}
			tmp = SystemUtil.millis() - start;
			if (tmp < res2) res2 = tmp;

			// (int)
			start = SystemUtil.millis();
			for (int i = 0; i < max; i++) {
				new StringBuilder(left.length() + right.length()).append(left).append(right).toString();
			}
			tmp = SystemUtil.millis() - start;
			if (tmp < res3) res3 = tmp;

			// concat
			start = SystemUtil.millis();
			for (int i = 0; i < max; i++) {
				left.concat(right);
			}
			tmp = SystemUtil.millis() - start;
			if (tmp < res4) res4 = tmp;

		}
		print.e("<init>():	" + res1);
		print.e("<init>(String):	" + res2);
		print.e("<init>(int):	" + res3);
		print.e("concat:		" + res4);
	}

gives me the following result

<init>():	13.766375005245209
<init>(String):	12.96975001692772
<init>(int):	11.805583000183105
concat:		17.216666996479034

so it is faster, but my open question ism how many instaces of StringBuilder will we have that the GC need to clean up, atm we win 6ms with 1'000'000 concats