Demonstrates heap allocation problem caused by reusing the internal char[] arrays (value) when String.substring() is called

StringTest.java

import com.sun.management.HotSpotDiagnosticMXBean;

import java.lang.management.ManagementFactory;

import javax.management.MBeanServer;

/**
 * Demonstrates heap allocation problem with String.substring()
 * 	http://mail.openjdk.java.net/pipermail/core-libs-dev/2012-May/010257.html
 *
 * The idea of taking heap dump programmatically is based on
 * 	https://blogs.oracle.com/sundararajan/entry/programmatically_dumping_heap_from_java
 *
 * @author lcsontos
 *
 */
public class StringTest {

	// This is the name of the HotSpot Diagnostic MBean
	private static final String HOTSPOT_BEAN_NAME =
		"com.sun.management:type=HotSpotDiagnostic";

	// field to store the hotspot diagnostic MBean 
	private static volatile HotSpotDiagnosticMXBean hotspotMBean;

	static void dumpHeap(String fileName, boolean live) {
		// initialize hotspot diagnostic MBean
		initHotspotMBean();
		try {
			hotspotMBean.dumpHeap(fileName, live);
		} catch (RuntimeException re) {
			throw re;
		} catch (Exception exp) {
			throw new RuntimeException(exp);
		}
	}

	// initialize the hotspot diagnostic MBean field
	private static void initHotspotMBean() {
		if (hotspotMBean == null) {
			synchronized (StringTest.class) {
				if (hotspotMBean == null) {
					hotspotMBean = getHotspotMBean();
				}
			}
		}
	}

	// get the hotspot diagnostic MBean from the
	// platform MBean server
	private static HotSpotDiagnosticMXBean getHotspotMBean() {
		try {
			MBeanServer server = ManagementFactory.getPlatformMBeanServer();
			HotSpotDiagnosticMXBean bean = 
				ManagementFactory.newPlatformMXBeanProxy(server,
				HOTSPOT_BEAN_NAME, HotSpotDiagnosticMXBean.class);
			return bean;
		} catch (RuntimeException re) {
			throw re;
		} catch (Exception exp) {
			throw new RuntimeException(exp);
		}
	}

	public static void main(String[] args) {

		final int len = 1 * 1024 * 1024;
		char[] value = new char[len];

		for (int i = 0; i < len; i++) {
			value[i] = (char)('A' + (i % 26));
		}

		String test = new String(value);

		test = test.substring(len - 10, len);

		System.out.println("test=" + test);

		final String fileName = "/tmp/" + System.currentTimeMillis() + ".hprof";

		dumpHeap(fileName, true);
	}
}