Java Examples: Starting a JVM with duplicate options

Question:

Which JVM option is used when there are duplicates

Answer:

In general, it's usually the latter option that gets used if the jvm doesn't reject it. I'm not sure if it is documented anywhere. Your best bet is to see what happens with your specific JVM, via Runtime's totalMemory and maxMemory:

Code:

public class HeapSize {
   public static final void main(String[] args) {
      Runtime rt = Runtime.getRuntime();
      System.out.println("Total currently: " + rt.totalMemory());
      System.out.println("Max:             " + rt.maxMemory());
   }
}

Output:

$ java HeapSize
Total currently: 94896128
Max:             1407713280

$ java -Xmx64m HeapSize
Total currently: 64487424
Max:             64487424

$ java -Xmx64m -Xmx512m HeapSize
Total currently: 94896128
Max:             477102080

$ java -Xmx512m -Xmx64m HeapSize
Total currently: 64487424
Max:             64487424