loop through field's values (or methods) of an object in java

The following example retrieves the field names of the concrete class (declaredField = fields declared by the class, (public)field = public fields declared by the class and it's super classes), derives a name of a corresponding getter from it (i.e. private String example -> getExample), searches for the method with the same name and invokes it on the instance m of Material

Material m = ...;
Stream.of(Material.class.getDeclaredFields())
      .map(field -> "get" + ucFirst(field.getName()))
      .map(getterName -> Material.class.getMethod(getterName))
      .map(getterMethod -> getterMethod.invoke(m))
      .forEach(fieldValue -> {
            //do something
      });

...
private String ucFirst(String input) {
    if(input.length() <= 1){
        return input.toUpperCase();
    }
    return input.substring(0, 1).toUpperCase() + input.substring(1);
}

(I removed the exception handling for better readability)

This is just one way to do it, there are many others. The same way you could access the toString method:

String toString = (String)Material.class.getMethod("toString").invoke(m);

Or you could get all the getter you want:

Stream.of(Material.class.getMethods())
      .filter(method -> method.getName().startsWith("get"))
      .map(getterMethod -> getterMethod.invoke(m))
      .forEach(fieldValue -> {
            //do something
      });

Note that getMethods will retrieve only public methods, but from all the super classes as well, while getDeclaredMethods will retrieve only method from the current classes. This may be important to know when dealing with the subclasses.