泛型的使用

public class Test {
    public static void main(String[] args) {
        Generics<String> g1 = new Generics<>();
        Generics<Integer> g2 = new Generics<>();
        Generics<Double> g3 = new Generics<>();
        
        g1.setValue("hello");
        g2.setValue(123);
        g3.setValue(3.14);
        
        printGenerics(g2);
        printGenerics(g3);
        
    }

    private static void printGenerics(Generics<? extends Number> g) {
        Number number = g.getValue();
        System.out.println(number);
    }
}

public class Generics<T> {
    private T value;

    public T getValue() {
        return value;
    }

    public void setValue(T value) {
        this.value = value;
    }
}