Java Utililty Methods Memory

List of utility methods to do Memory

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Description

The list of methods to do Memory are organized into topic(s).

Method

longalignMemory(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;
booleancheckLowMemory()
check Low Memory 
return checkLowMemory(0.2);
longcheckMemory()
check Memory 
return (Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory());
voidcheckMinMemory(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);
voidcompactMemory()
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();
...
longcorrectMemoryValue(int memory)
correct Memory Value 
long mem = memory;
if (mem < 0) {
    mem -= Integer.MIN_VALUE;
    mem += Integer.MAX_VALUE;
return mem;
voiddisplayMemory(String label, long bytes)
display Memory 
long memoryKBytes = bytes / 1024;
long memoryMBytes = memoryKBytes / 1024;
System.out.println(label + " = " + bytes + " bytes, " + memoryKBytes + "KB, " 
        + memoryMBytes + "MB");
voiddumpMemory()
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");
voiddumpMemoryInfo(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) {
...
ObjectfillMemory()
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;