JAVA EE: Java Tutorial : Java String vs StringBuffer vs StringBuilder(memory test)

Wednesday 11 May 2016

Java Tutorial : Java String vs StringBuffer vs StringBuilder(memory test)

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StringMemoryTest.java

public class StringMemoryTest
{

    private static final int KBinBytes = 1024;

    /**
     * Perform GC
     */
    private void performGC()
    {
        for (int i = 0; i < 10; i++)
        {
            System.gc();
            try
            {
                Thread.sleep(100);
            }
            catch (InterruptedException e)
            {
                Thread.currentThread().interrupt();
            }
        }
    }

    /**
     * Get the memory used value.
     * 
     * @return long
     */
    private long memoryUsed()
    {
        return ((Runtime.getRuntime().totalMemory() / KBinBytes) - (Runtime
                .getRuntime().freeMemory() / KBinBytes));
    }

    /**
     * Method to test String object memory consumption in a
     * BIG loop
     */
    public void testStringMemory()
    {
        System.out
                .println("Initial Total memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().totalMemory()
                        / KBinBytes);
        System.out
                .println("Initial Free memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().freeMemory()
                        / KBinBytes);
        long initialmemory = memoryUsed();
        long startTime = System.currentTimeMillis();
        String str = "";
        for (int i = 1; i < 50000; i++)
        {
            str = str + "Hello";
        }
        long stopTime = System.currentTimeMillis();
        long elapsedTime = stopTime - startTime;
        System.out.println("Time taken to complete the process in MilliSeconds:"
                + elapsedTime);

        System.out.println("Memory used by String in KBs="
                + (memoryUsed() - initialmemory));
        str = null;
        performGC();
        System.out.println("Free Memory after GC in KBs="
                + Runtime.getRuntime().freeMemory() / KBinBytes);

    }

    /**
     * Method to test StringBuilder object memory
     * consumption in a BIG loop
     */
    public void testStringBuilderMemory()
    {
        System.out
                .println("Initial Total memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().totalMemory()
                        / KBinBytes);
        System.out
                .println("Initial Free memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().freeMemory()
                        / KBinBytes);
        long initialmemory = memoryUsed();
        long startTime = System.currentTimeMillis();
        StringBuilder sb = new StringBuilder();
        for (int i = 1; i < 50000; i++)
        {
            sb.append("Hello");
        }
        long stopTime = System.currentTimeMillis();
        long elapsedTime = stopTime - startTime;
        System.out
                .println("Time taken to complete the process in MilliSeconds:"
                        + elapsedTime);
        System.out.println("Memory used by StringBuilder in KBs="
                + (memoryUsed() - initialmemory));
        sb = null;
        performGC();
        System.out.println("Free Memory after GC in KBs="
                + Runtime.getRuntime().freeMemory() / KBinBytes);

    }

    /**
     * Method to test StringBuffer object memory consumption
     * in a BIG loop
     */
    public void testStringBufferMemory()
    {
        System.out
                .println("Initial Total memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().totalMemory()
                        / KBinBytes);
        System.out
                .println("Initial Free memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().freeMemory()
                        / KBinBytes);
        long initialmemory = memoryUsed();
        long startTime = System.currentTimeMillis();
        StringBuffer sb = new StringBuffer();

        for (int i = 1; i < 50000; i++)
        {
            sb.append("Hello");
        }
        long stopTime = System.currentTimeMillis();
        long elapsedTime = stopTime - startTime;
        System.out.println("Time taken to complete the process in MilliSeconds:"
                + elapsedTime);
        System.out.println("Memory used by StringBuffer in KBs="
                + (memoryUsed() - initialmemory));
        sb = null;
        performGC();
        System.out.println("Free Memory after GC in KBs="
                + Runtime.getRuntime().freeMemory() / KBinBytes);

    }

    /**
     * Main class
     * 
     * @param args
     */
    public static void main(String[] args)
    {
        System.out
                .println("Initial Max memory in Java virtual machine in KBs="
                        + Runtime.getRuntime().maxMemory()
                        / KBinBytes);
        StringMemoryTest memoryTest = new StringMemoryTest();
        System.out.println(".....................................................\nString memory test\n");
        memoryTest.testStringMemory();
        System.out.println(".................................................\nStringBuffer memory test\n");
        memoryTest.testStringBufferMemory();
        System.out.println("...............................................\nStringBuilder memory test\n");
        memoryTest.testStringBuilderMemory();

    }

}

Output

Initial Max memory in Java virtual machine in KBs=919552
...........................................................
String memory test

Initial Total memory in Java virtual machine in KBs=62976
Initial Free memory in Java virtual machine in KBs=61992
Time taken to complete the process in MilliSeconds:7729
Memory used by String in KBs=130666
Free Memory after GC in KBs=349431
...........................................................
StringBuffer memory test

Initial Total memory in Java virtual machine in KBs=355840
Initial Free memory in Java virtual machine in KBs=349431
Time taken to complete the process in MilliSeconds:11
Memory used by StringBuffer in KBs=0
Free Memory after GC in KBs=348918
............................................................
StringBuilder memory test

Initial Total memory in Java virtual machine in KBs=355328
Initial Free memory in Java virtual machine in KBs=348918
Time taken to complete the process in MilliSeconds:5
Memory used by StringBuilder in KBs=0
Free Memory after GC in KBs=348406