Java8新特性

1 Lambda表达式

1.1 使用Lambda表达式实现函数式接口1

【案例1】函数是接口 MyInterOne

//函数式接口（接口中只有一个抽象方法）
@FunctionalInterface
public interface MyInterOne {
    public abstract void methodOne();
}

【案例2】定义MyInterOneImpl类实现接口MyInterOne

public class MyInterOneImpl implements MyInterOne {
    @Override
    public void methodOne() {
        System.out.println("in MyInterOneImpl methodOne()~~~~~~~~~~~~~~~");
    }
}

【案例3】

public class TestOne {
    public static void main(String[] args) {
        MyInterOne myInterOne = new MyInterOneImpl();
        //0.创建对象调用方法
        myInterOne.methodOne();

        //1.内部类实现接口
        MyInterOne myInterTwo = new MyInterOne() {
            @Override
            public void methodOne() {
                System.out.println("in innerClass methodOne()~~~~~~~~~~~~~~~~");
            }
        };
        myInterTwo.methodOne();

        //2.lambda表达式只能用于实现函数式接口
        MyInterOne myInterThree = () -> {System.out.println("in lambda methodOne()~~~~~~~~~~~~~~~~~~~~~~~");};
        myInterThree.methodOne();
    }
}

 

1.2 使用Lambda表达式实现函数式接口2

【案例1】多个接口，方法分别无参、有一个参数、多个参数

// 函数式接口(接口中只有一个抽象方法)
@FunctionalInterface
public interface MyInterOne {
    public abstract void methodOne();
}

@FunctionalInterface
interface MyInterTwo{
    public abstract void methodTwo(String s);
}

@FunctionalInterface
interface MyInterThree{
    public abstract void methodThree(String s,int i);
}

【案例2】

public class TestTwo {
    public static void main(String[] args) {
        // 函数式实现接口的几种方式
        MyInterOne myInterOne = new MyInterOne() {
            @Override
            public void methodOne() {
                System.out.println("in innerClass methodOne~~~~~~~~~~~~~~~~~");
            }
        };
        myInterOne.methodOne();

        // lambda表达式实现
        //1.接口中的方法 无参
        //1.1 如果方法的实现体有多行代码，则必须保留方法大括号
        MyInterOne myInterOne1 = () -> {
            System.out.println("in myInterTwo methodOne~~~~~~~~~~~~~~~~~~~~~");
        };
        myInterOne.methodOne();
        //1.2 如果方法的实现只有一行代码，则可以省略大括号
        MyInterOne myInterOne2 = () -> System.out.println("in myInterTwo methodOne~~~~~~~~~~~~~~~~~");
        myInterOne2.methodOne();

        //2.单个形参情况下
        //2.1 形参给出类型和形参名
        MyInterTwo myInterTwo = (String s) -> System.out.println(s);
        myInterTwo.methodTwo("hello world1");
        //2.2 形参可以不给类型，只给形参名
        MyInterTwo myInterTwo1 = (s) -> System.out.println(s);
        myInterTwo1.methodTwo("hello world2");
        //2.3 如果形参只有一个参数，则可以省略小括号
        MyInterTwo myInterTwo2 = s -> System.out.println(s);
        myInterTwo2.methodTwo("hello world3");

        // 3.多个形参情况下
        // 3.1给出每个参数的参数类型和参数名
        MyInterThree myInterThree = (String s,int i) -> System.out.println("s="+s+",i="+i);
        myInterThree.methodThree("hello",101);
        // 3.2给出每个参数形参名，省略形参类型
        MyInterThree myInterThree1 = (s,i) -> System.out.println("s="+s+",i="+i);
        myInterThree1.methodThree("ok",202);

    }
}

 

1.3 使用Lambda表达式实现函数式接口3