how to get a constant in java with class

If this constant is metadata about the class, I'd do this with annotations:

First step, declare the annotation:

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@interface Abc {
    String value(); 
}

Step two, annotate your class:

@Abc("Hello, annotations!")
class Zomg {

}

Step three, retrieve the value:

String className = "com.example.Zomg";
Class<?> klass = Class.forName(className);
Abc annotation = klass.getAnnotation(Abc.class);
String abcValue = annotation.value();
System.out.printf("Abc annotation value for class %s: %s%n", className, abcValue);

Output is:

Abc annotation value: Hello, annotations!

You might look for sth. like
Foo.class.getDeclaredField("THIS_IS_MY_CONST").get(null); or Class.forName("Foo").getDeclaredField("THIS_IS_MY_CONST").get(null); (thanks f-o-o)

Gets the value of a String constant (THIS_IS_MY_CONST) in class Foo.

Update use null as argument for get thanks acdcjunior