when the HashMap instance need synchronized?

[shi yongfei]

an class will be run under a mutilthreaded environ,the class like this
public class ReportEngine
{
private HashMap publicReport;
private Report getReportData(String reportKey) {
return publicReport.get(reportKey);
}
private void deleteReport(String reportKey) {
publicReport.remove(reportKey);
}
private void addReport(String reportKey,Report report) {
publicReport.add(reportKey,report);
}
}
So, what I am puzzled are:
1)which methods need synchronized ?
2)what will happen if don't synchronize any methods ?

[Kao-Wei Wan]

1)which methods need synchronized ?
Both deleteReport and addReport
2)what will happen if don't synchronize any
methods ?
your program may lost data or crush

[Philip Hung]

You could also replace the HashMap with a Hashtable unless you specifically want a HashMap or you are permitting null values.

[Jim Yingst]

Ugh. Let Hashtable die the death it deserves (along with Vector and Enumeration). There's no need for those things anymore; they just create additional opportunities for confusion, particularly for newbies. If you really want a synchronized Map, use Collections.synchronizedMap(new HashMap()). And pay attention to the warnings about iterating - these would have applied to Hashtable too.

[Dana Hanna]

******** Use a synchronized HashMap - Collections.synchronizedMap(new HashMap());
Also - the get method would also have to be synchronized if for some reason you don't want a synchronized map (why not?). This is because the HaspMap could be resizing itself during the get operation and really throw it off.