external program from java doesn't terminate

Question

When I try to execute an external program from java I use this code below :

Process p;
rn = Runtime.getRuntime();

String[] unzip = new String[2];

unzip[0]="unzip";

unzip[1]=archive ;

public void dezip() throws IOException{

    p = rn.exec(unzip);
    int ret = p.exitValue();

System.out.println("End of unzip method");

But my last System.out is never executed, as if we exit from unzip method. The unzip() call does only the half of the work, only a part of my archive is unzipped. When I use ps -x or htop from command line I see that unzip process is still here.

Help please.