1.遍历map

void testMap() {        Map
     
       map = new HashMap<>();        map.put("a", 1);        map.put("b", 1);        map.put("c", 1);        map.forEach((k, v)-> System.out.println(k + ":" + v));    }
     

输出

a:1b:1c:1

2.遍历带lambda条件的map

void testMapLambda() {        Map
     
       map = new HashMap<>();        map.put("a", 1);        map.put("b", 1);        map.put("c", 1);        map.forEach((k, v)-> {            if ("b".equalsIgnoreCase(k)) {                System.out.println(k + ":" + v);            }        });    }
     

输出

b:1

3.遍历带lambda条件的list

void testList() {        List
     
       list = new ArrayList<>();        list.add("abc");        list.add("def");        list.add("hij");        list.forEach(key -> {                    if ("def".equalsIgnoreCase(key)) {                        System.out.println(key);                    }                }        );    }
     

输出

def

Lambda表达式局部变量

示例

public class LambdaTest {    int instanceCounter = 0;    public void method() {        int localCounter = 0;        instanceCounter = 5; //Re-assign instance counter so it is no longer effectively final        Stream.of(1,2,3).forEach(elem -> instanceCounter++); //WHY DOES THE COMPILER NOT COMPLAIN HERE        Stream.of(1,2,3).forEach(elem -> localCounter++); //Does not compile because localCounter is not effectively final    }}

其中instanceCounter是类的成员变量，localCounter是函数的局部变量，在标红的语句报错