Lambda表達(dá)式的應(yīng)用

Lambda表達(dá)式的應(yīng)用

調(diào)用Collection.sort()方法，通過(guò)定制排序比較兩個(gè)Employee(先按年齡比，年齡相同按姓名比)，使用Lambda作為參數(shù)傳遞

List<Employee> employees = Arrays.asList(
            new Employee("張三", 18 ,9999.99),
            new Employee("李四", 50, 5555.99),
            new Employee("王五", 50, 6666.66),
            new Employee("趙六", 16, 3333.33),
            new Employee("田七", 8, 7777.77)
    );

    @Test
    public void test1(){
        Collections.sort(employees, (e1, e2) -> {
            if (e1.getAge() == e2.getAge()){
                return e1.getName().compareTo(e2.getName());
            }else {
                return Integer.compare(e1.getAge(), e2.getAge());
                //倒序排
                //return -Integer.compare(e1.getAge(), e2.getAge());
            }
        });

        for (Employee employee : employees){
            System.out.println(employee);
        }
    }

1. 聲明函數(shù)式接口，接口中聲明抽象方法，public String getValue(String str);

2. 聲明類TestLambda，類中編寫方法使用接口作為參數(shù)，將一個(gè)字符串轉(zhuǎn)換為大寫，并作為方法的返回值

3. 再將一個(gè)字符串的第2個(gè)和第4個(gè)索引位置進(jìn)行截取子串

@FunctionalInterface
public interface MyFunction {

    public String getValue(String str);
}

List<Employee> employees = Arrays.asList(
            new Employee("張三", 18 ,9999.99),
            new Employee("李四", 50, 5555.99),
            new Employee("王五", 50, 6666.66),
            new Employee("趙六", 16, 3333.33),
            new Employee("田七", 8, 7777.77)
    );

    //需求：用于處理字符串
    public String strHandler(String str, MyFunction mf){
        return mf.getValue(str);
    }

    @Test
    public void test2(){
        String trimStr = strHandler("abfdfdf", (str) -> str.toUpperCase());
        System.out.println(trimStr);

        String subStr = strHandler("abfdfdf", (str) -> str.substring(2, 4));
        System.out.println(subStr);

    }

1. 聲明一個(gè)帶兩個(gè)泛型的函數(shù)式接口，泛型類型為<T, R> T為參數(shù)，R為返回值

2. 接口中聲明對(duì)應(yīng)抽象方法

3. 使用接口作為參數(shù)，計(jì)算兩個(gè)long類型參數(shù)的和

4. 再計(jì)算兩個(gè)long型參數(shù)的乘積

public interface MyFunction2<T, R> {

    public R getValue(T t1, T t2);
}

//需求：對(duì)于兩個(gè)Long型數(shù)據(jù)進(jìn)行處理
    public void op(Long l1, Long l2, MyFunction2<Long, Long> mf){
        System.out.println(mf.getValue(l1, l2));
    }

    @Test
    public void test3(){
        op(100L, 200L, (x, y) -> x + y);

        op(100L, 200L, (x, y) -> x * y);
    }