TimePrinter接口：

@FunctionalInterface
public interface CurrentTimePrinter

{
    void printCurrenTime();
}

测试类：

public class Test01 {
    public static void main(String[] args) {
        showLongTime(()->System.out.println(System.currentTimeMillis()));
    }

    public static void showLongTime(CurrentTimePrinter timePrinter){
        timePrinter.printCurrentTime();
    }
}

IntCalc接口：

@FunctionalInterface
public interface IntCalc {
    int calc(int a, int b);
}

测试类：

public class Test02 {
    public static void main(String[] args) {
        getProduct(2,3,(a,b)->a*b);
    }
    public static void getProduct(int a, int b, IntCalc intCalc){
        int product = intCalc.calc(a,b);
        System.out.println(product);

    }
}

NumberToString接口：

@FunctionalInterface
public interface NumberToString {
    String convert(int num);
}

测试类：

public class Test03 {
    public static void main(String[] args) {
        decToHex(999, Integer::toHexString);
    }
    public static void decToHex(int num ,NumberToString nts){
        String convert = nts.convert(num);
        System.out.println(convert);
    }
}