HashMapTest.java uses unchecked or unsafe operations.

[jeer]

Hi

I am new to Java. m using HashMap class.
when i compile "javac HashMapTest.java", i get following error:
Note: HashMapTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

I was using:
HashMap h= new HashMap();

I made some changes in my code
import java.util.*;
public class HashMapTest {
public static void main(String[] args) {
// creating HashMap object
HashMap<String,Object> h= new HashMap<String,Object>();
// creating Student objects
Student s1 = new Student ("ali" , 1);
// adding elements (Student objects) where roll nos
// are stored as keys and student objects as values
h.put("one", s1);
............
........
.....

Now, after compile, there is no error but when i run my code then there is following exception:
Exception in thread "main" java.lang.UnsupportedClassVersionError: HashMapTest
(Unsupported major.minor version 49.0)
at java.lang.ClassLoader.defineClass0(Native Method)
at java.lang.ClassLoader.defineClass(Unknown Source)
at java.security.SecureClassLoader.defineClass(Unknow n Source)
at java.net.URLClassLoader.defineClass(Unknown Source)
at java.net.URLClassLoader.access$100(Unknown Source)
at java.net.URLClassLoader$1.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at sun.misc.Launcher$AppClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClass(Unknown Source)
at java.lang.ClassLoader.loadClassInternal(Unknown Source)


Please guide me to resolve this error
Cheers

[Eranga]

What ArrayListTest class doing there in your application?

[rjuyal]

working fine in my system:

where is ArrayListTest class

[Eranga]

Yep, he has something wrong with that class. Seems to he used some class libraries which are not supported with currently working version.

[jeer]

Sorry, that is HashMapTest

[rjuyal]

Oh man, you have edited the compilation error

[Eranga]

In that case, your code is ok. Except that you work out correctly on the Student object. Constructor parameters...

[jeer]

My Student class looks fine, following is the code:

public class Student {
private String name;
private int rollNo;
// Standard Setters
public void setName (String name) {
this.name = name;
}
// Note the masking of class level variable rollNo
public void setRollNo (int rollNo) {
if (rollNo > 0) {
this.rollNo = rollNo;
}else {
this.rollNo = 100;
}
}
// Standard Getters
public String getName ( ) {
return name;
}
public int getRollNo ( ) {
return rollNo;
}
// Default Constructor
public Student() {
name = "not set";
rollNo = 100;
}
// parameterized Constructor for a new student
public Student(String name, int rollNo) {
setName(name); //call to setter of name
setRollNo(rollNo); //call to setter of rollNo
}
// Copy Constructor for a new student
public Student(Student s) {
name = s.name;
rollNo = s.rollNo;
}
// method used to display method on console
public void print () {
System.out.print("Student name: " +name);
System.out.println(", roll no: " +rollNo);
}
} // end of class

[Eranga]

Everything working fine for me. Which Java version you used?

[rjuyal]

set

JAVA_HOME to the directory having latest JDK version

also
in your path variable replace all occurence of older path to new one.


one more thing, what do it return
java - version

[Eranga]

Rakesh, you talking to me. If so, now it's useless, because all the things perfect for any version.

[rjuyal]

Sorry! i replied to jeer

i guess he compiled with 1.5 version and running with 1.4

[jeer]

I have installed jdk1.5.0_14.
I have already included "C:\Program Files\Java\jdk1.5.0_14\bin;" in path environment variable.
how can i set JAVA_HOME?

[Eranga]

I thought it's for me.

What the point with 1.4 Rakesh. Only the HashMap he used in advanced. But it support from 1.2. So...

[rjuyal]

i don't think JAVA code compiled with 1.5 will run using 1.4 version ( for all cases ) may be i am wrong.

if he have used some methods which were only in 1.5 , and not in 1.4 in that case it should certainly not run

[Eranga]

Quote:

Originally Posted by rjuyal

i don't think JAVA code compiled with 1.5 will run using 1.4 version ( for all cases ) may be i am wrong.

You are 100% correct. May be confused with my last replay. What I try to say is this.

Some functions(libraries and so..) on later versions are not supported in newer versions. Basically Suns' deprecate them newer versions in different way. Only such thing I can see from our original code is the HashMap, supported from 1.2 and I think my numbers are correct.

[rjuyal]

HashMap<String,Object> h

this feature was not in 1.4
in 1.4 we have to write:

HashMap h


BTW, i don't remember what do we say this feature <String,Object>

[rjuyal]

we call it Generics

[jeer]

I am compiling and running my code using same java version. if i use
HashMap h
then there following error:
Note: HashMapTest.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

[rjuyal]

Uses unchecked or unsafe operations message