Java Utililty Methods Memory

long alignMemory(long numBytes)
Most current VMs have memory alignment that places objects into heap space that is a multiple of 8 Bytes.

long remainder = numBytes % 8;
if (remainder != 0) {
 numBytes += (8 - remainder);
return numBytes;

boolean checkLowMemory()
check Low Memory

return checkLowMemory(0.2);

long checkMemory()
check Memory

return (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory());

void checkMinMemory(long min)
Exits with code -1 if maximum memory is below 90% of minimally allowed threshold.

long maxMem = Runtime.getRuntime().maxMemory();
if (maxMem < .85 * min) {
 System.err.println("Heap limit is too low (" + (maxMem / (1024 * 1024))
 + "MB), please increase heap size at least up to " + (min / (1024 * 1024)) + "MB.");
 System.exit(-1);

void compactMemory()
Compacts memory as much as possible by allocating huge memory block and then forcing garbage collection.

try {
 final byte[][] unused = new byte[128][];
 for (int i = unused.length; i-- != 0;) {
 unused[i] = new byte[2000000000];
} catch (OutOfMemoryError ignore) {
System.gc();
...

long correctMemoryValue(int memory)
correct Memory Value

long mem = memory;
if (mem < 0) {
 mem -= Integer.MIN_VALUE;
 mem += Integer.MAX_VALUE;
return mem;

void displayMemory(String label, long bytes)
display Memory

long memoryKBytes = bytes / 1024;
long memoryMBytes = memoryKBytes / 1024;
System.out.println(label + " = " + bytes + " bytes, " + memoryKBytes + "KB, " 
 + memoryMBytes + "MB"); 

void dumpMemory()
dump Memory

System.out.println("\n" + "Max. memory: " + Runtime.getRuntime().maxMemory() / 1024 / 1024 + " MB" + "\n"
 + "Tot. memory: " + Runtime.getRuntime().totalMemory() / 1024 / 1024 + " MB" + "\n"
 + "Free memory: " + Runtime.getRuntime().freeMemory() / 1024 / 1024 + " MB");

void dumpMemoryInfo(String msg)
Dumps out memory information

Runtime rt = Runtime.getRuntime();
long free = rt.freeMemory();
rt.gc();
long reclaimedMemory = (rt.freeMemory() - free) / (1024 * 1024);
long freeMemory = rt.freeMemory() / (1024 * 1024);
long totalMemory = rt.totalMemory() / (1024 * 1024);
long usedMemory = rt.totalMemory() - rt.freeMemory();
if (usedMemory > maxUsed) {
...

Object fillMemory()
Fills memory and returns an object that refers to all of what was allocated.

byte[][] arrays = new byte[100][];
int size = 1 << 30;
int idx = 0;
while (true) {
 try {
 while (true) {
 arrays[idx++] = new byte[size];
 } catch (OutOfMemoryError oome) {
 if (size == 0) {
 break;
 } else {
 size /= 2;
return arrays;