[Solved] best Java code to control big heap memeory used (like 1G) [closed]

by


Quickly allocate 1 GB of memory:

byte[][] memoryWaster = new byte[1024][1_048_576];

See last test run below for successful allocation of 16 GB of memory.

Test program

Runtime runtime = Runtime.getRuntime();
System.out.printf("total: %11d   max: %d%n", runtime.totalMemory(), runtime.maxMemory());
System.out.printf("used:  %11d%n", runtime.totalMemory() - runtime.freeMemory());
System.gc();
System.out.printf("gc:    %11d%n", runtime.totalMemory() - runtime.freeMemory());
byte[][] memoryWaster = new byte[1024][1_048_576];
memoryWaster[0][0] = 2; // prevent unused warning
System.out.printf("new[]: %11d%n", runtime.totalMemory() - runtime.freeMemory());
System.gc();
System.out.printf("gc:    %11d%n", runtime.totalMemory() - runtime.freeMemory());
memoryWaster = null;
System.out.printf("null:  %11d%n", runtime.totalMemory() - runtime.freeMemory());
System.gc();
System.out.printf("gc:    %11d%n", runtime.totalMemory() - runtime.freeMemory());

Output (Java 8, 32-bit):

// Java 1.8.0_51, 32-bit, no -Xmx given
total:    16252928   max: 259522560
used:       543288
gc:         349296
Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
        at test.Test.main(Test.java:11)

// Java 1.8.0_51, 32-bit, -Xmx1200m
total:    16252928   max: 1216348160
used:       543288
gc:         349296
new[]:  1078435312
gc:     1078382592
null:   1078382592
gc:       15711288

// Java 1.8.0_51, 64-bit, no -Xmx given, 32 GB machine
total:   514850816   max: 7618953216
used:      5389872
gc:        2981048
new[]:  1074961632
gc:     1081175720
null:   1081175720
gc:       13027424

// Java 1.8.0_51, 64-bit, -Xmx1200m
total:   514850816   max: 1118830592
used:      5389872
gc:        2981048
new[]:  1077948560
gc:     1078944096
null:   1078944096
gc:        3501136

// Java 1.8.0_51, 64-bit, -Xmx20g, new byte[16384][1_048_576]
total:   514850816   max: 19088801792
used:      5389872
gc:        2981048
new[]: 17205604928
gc:    17205604928
null:  17205604928
gc:       26186032

2

solved best Java code to control big heap memeory used (like 1G) [closed]