BiConsumer or Consumer in Java8 - java-8

Question

I'm trying to understand/learn Consumer/BiConsumer in Java8.
test1 and test2 methods are working fine.
But if I tried to use the old fashion way by implementing BiConsumer in a class in test3 method.
And then override accept method in the class, str.substring method cannot resolve the method substring.
Can't I use the old fashion way in #FunctionalInterface or did I do something wrong in the code?
public class BiConsumerTest {
static void test1(String name, Integer count) {
method1(name, count, (str, i) -> {
System.out.println(str.substring(i));
});
}
static void test2(String name, Integer count) {
BiConsumer<String, Integer> consumer = (str, i) -> {
System.out.println(str.substring(i));
};
method1(name, count, consumer);
}
private static void method1(String name, Integer count, BiConsumer<String, Integer> consumer) {
consumer.accept(name, count);
}
private void test3(String name, Integer count) {
BiConsumer<String, Integer> consumer = new ConsumerImpl<String, Integer>();
consumer.accept(name, count);
}
class ConsumerImpl<String, Integer> implements BiConsumer<String, Integer> {
#Override
public void accept(String str, Integer count) {
str.substring(count); // str cannot find substring method !!!
}
}
public static void main(String[] args) {
String name = "aaa bbb ccc";
Integer count = 6;
test1(name, count);
test2(name, count);
}
}

Answer 1

You cannot define a class with known types as type-parameters (so this is incorrect - ConsumerImpl<String, Integer>). Plus there were few other syntactical mistakes. Below works -
import java.util.function.BiConsumer;
public class TestClass {
static void test1(String name, Integer count) {
method1(name, count, (str, i) -> {
System.out.println(str.substring(i));
});
}
static void test2(String name, Integer count) {
BiConsumer<String, Integer> consumer = (str, i) -> {
System.out.println(str.substring(i));
};
method1(name, count, consumer);
}
private static void method1(String name, Integer count, BiConsumer<String, Integer> consumer) {
consumer.accept(name, count);
}
static void test3(String name, Integer count) {
BiConsumer<String, Integer> consumer = new ConsumerImpl();
consumer.accept(name, count);
}
static class ConsumerImpl implements BiConsumer<String, Integer> {
#Override
public void accept(String str, Integer count) {
System.out.println(str.substring(count)); // str cannot find substring method !!!
}
}
public static void main(String[] args) {
String name = "aaa bbb ccc";
Integer count = 6;
test1(name, count);
test2(name, count);
test3(name, count);
}
}