JIT compiler and performance

public class Main {
    static int validateCalls, couponCalls, reportCalls;

    static boolean validate(int amount) { validateCalls++; return amount > 0; }
    static int coupon(int amount) { couponCalls++; return amount / 10; }
    static void report() { reportCalls++; }

    static void show(String name, int calls) {
        System.out.println(name + ": " + calls + " calls" + (calls > 200 ? "  <- hot, will be compiled" : ""));
    }

    public static void main(String[] args) {
        for (int order = 1; order <= 500; order++) {
            if (validate(order * 100) && order % 4 == 0) {
                coupon(order * 100);
            }
        }
        report();
        show("validate", validateCalls);
        show("coupon  ", couponCalls);
        show("report  ", reportCalls);
    }
}

public class Main {
    public static void main(String[] args) {
        String line = "     36    9       4       Main::gst (6 bytes)";
        String[] p = line.trim().split("\\s+");
        String[] tierNames = {"interpreter", "C1, no profiling", "C1, light profiling",
                              "C1, full profiling", "C2, fully optimised"};
        int tier = Integer.parseInt(p[2]);
        System.out.println("time:       " + p[0] + " ms after start");
        System.out.println("compile id: " + p[1]);
        System.out.println("tier:       " + tier + " = " + tierNames[tier]);
        System.out.println("method:     " + p[3]);
        System.out.println("bytecode:   " + p[4].substring(1) + " bytes");
    }
}

public class Main {
    public static void main(String[] args) {
        String[] log = {
            "35    8       3       Main::gst (6 bytes)",
            "36    9       4       Main::gst (6 bytes)",
            "36    8       3       Main::gst (6 bytes)   made not entrant",
            "38   10 %     3       Main::main @ 4 (36 bytes)",
            "39   11       3       Main::main (36 bytes)",
            "39   12 %     4       Main::main @ 4 (36 bytes)",
            "42   10 %     3       Main::main @ 4 (36 bytes)   made not entrant"
        };
        int normal = 0, osr = 0, discarded = 0;
        for (String line : log) {
            if (line.contains("made not entrant")) discarded++;
            else if (line.contains(" % ")) osr++;
            else normal++;
        }
        System.out.println("Normal compilations: " + normal);
        System.out.println("OSR compilations:    " + osr);
        System.out.println("Old code discarded:  " + discarded);
    }
}

public class Main {
    static int discount(int price) {
        return price > 1000 ? price / 10 : 0;
    }

    public static void main(String[] args) {
        long checksum = 0;
        for (int price = 1; price <= 100_000; price++) {
            checksum += discount(price);      // result is used
        }
        System.out.println("Checksum: " + checksum);
    }
}

public class Main {
    public static void main(String[] args) {
        long[] rounds = {4551, 2228, 1217, 1198, 819, 557, 561, 549, 553, 560};
        int warmup = 4;
        long all = 0, steady = 0;
        for (int i = 0; i < rounds.length; i++) {
            all += rounds[i];
            if (i >= warmup) steady += rounds[i];
        }
        double naive = (double) all / rounds.length;
        double steadyAvg = (double) steady / (rounds.length - warmup);
        System.out.printf("Naive average:  %.1f us%n", naive);
        System.out.printf("Steady average: %.1f us%n", steadyAvg);
        System.out.printf("First round was %.1fx slower than steady state%n", rounds[0] / steadyAvg);
    }
}

public class Main {
    public static void main(String[] args) {
        long primitiveTotal = 0;
        Long boxedTotal = 0L;
        for (int i = 0; i < 100_000; i++) {
            long amount = (i % 500 + 1) * 100L;
            primitiveTotal += amount;
            boxedTotal += amount;          // unbox, add, box a new Long
        }
        System.out.println("long total: Rs " + primitiveTotal / 100);
        System.out.println("Long total: Rs " + boxedTotal / 100);
        System.out.println("Same? " + (primitiveTotal == boxedTotal));
    }
}

public class Main {
    static void summary(String name, int[] ms) {
        int sum = 0, worst = 0;
        for (int t : ms) {
            sum += t;
            worst = Math.max(worst, t);
        }
        System.out.printf("%s average %.1f ms, worst %d ms%n", name, (double) sum / ms.length, worst);
    }

    public static void main(String[] args) {
        int[] first = {180, 150, 96, 88, 61, 47, 40, 33, 30, 28};
        int[] later = {22, 21, 23, 20, 22, 21, 24, 22, 21, 23};
        summary("First 10:", first);
        summary("Next 10: ", later);
        System.out.println("Needs warm-up before traffic? " + (first[0] > 3 * later[0] ? "yes" : "no"));
    }
}