Java memory allocation

The Java Virtual Machine takes two command line arguments which set the initial and maximum heap sizes: -Xms and -Xmx.
 You can add a system environment variable named _JAVA_OPTIONS (under Windows), and set the heap size values there.
For example if you want a 512Mb initial and 1024Mb maximum heap size you could use:
 
SET _JAVA_OPTIONS = -Xms512m -Xmx1024m
 
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It is possible to increase heap size allocated by the JVM by using command line options Here we have 3 options
 
-Xms<size>        set initial Java heap size
-Xmx<size>        set maximum Java heap size
-Xss<size>        set java thread stack size
 
java -Xms16m -Xmx64m ClassName