Java8-Lambda语法 Lambda表达式一、lambda语法参数列表 lambda body部分 (o1,o2)->o1.getWeight().compareTo(o2.getWeight());二、 合法lamdba表达式1、s -> s.length(); 或者 (String s) -> s.length(); 2、apple -> apple.getColor().equals("great"); 或者 (Apple apple) -> apple.getColor().equals("great"); 3、(int x, int y) -> { System.out.println(x); System.out.println(y); }; 4、() -> 12; 5、()-{}; 6、()->“hello” 或者 ()->{return "hello"}三、语法总结语法一、（参数列表） -> 表达式 语法二、（参数列表） -> {语句;}有效lambda表达式1、() -> {} 2、() -> "hello" 或者 ()->{reurn "hello"} 3、(String str) -> {return "hello"} 或者 (String str) -> "hello";无效lambda表达式(integer i)->{return "错误示范"+i}四、代码说明package com.example.study.java8.InterfaceFunction; import java.util.Arrays; import java.util.Comparator; import java.util.List; import java.util.concurrent.Callable; import java.util.function.Function; import java.util.function.Predicate; /** * lambda语法 */ public class LambdaExpression { public static void main(String[] args) { Comparator<Apple> colorComparator = new Comparator<Apple>() { @Override public int compare(Apple o1, Apple o2) { return o1.getColor().compareTo(o2.getColor()); } }; List<Apple> apples = Arrays.asList(new Apple("a", 18), new Apple("c", 20), new Apple("b", 10)); for (Apple a : apples) { System.out.println(a.toString()); } System.out.println("================================="); apples.sort(colorComparator); for (Apple a : apples) { System.out.println(a.toString()); } System.out.println("================================="); //lambda expression //方法推导：接口有返回值时，注意lambda有大括号{}，必须要有return，没有可以不用使用return关键词 //1、有{},必须使用return Comparator<Apple> weightComparator = (o1, o2) -> { return o1.getWeight().compareTo(o2.getWeight()); }; //2、不使用{}，没有return Comparator<Apple> weightComparator2 = (o1, o2) -> o1.getWeight().compareTo(o2.getWeight()); apples.sort(weightComparator); for (Apple a : apples) { System.out.println(a.toString()); } //合法lambda表达式格式1 Function<String, Integer> stringIntegerFunction = s -> s.length(); //合法lambda表达式格式2 Predicate<Apple> great = (Apple apple) -> apple.getColor().equals("great"); Predicate<Apple> great2 = apple -> apple.getColor().equals("great"); //合法lambda表达式格式3 // (int x, int y) -> { // System.out.println(x); // System.out.println(y); // }; //合法lambda表达式格式4 Callable<Integer> integerCallable = () -> 12; //合法lambda表达式格式5 Runnable runnable = () -> { }; //合法lambda表达式格式6 Callable<String> stringCallable = () -> "hello"; //合法lambda表达式格式7 Function<String, String> stringStringFunction = (String str) -> { return "hello"; }; //合法lambda表达式格式8 Function<String, String> stringStringFunction1 = (String str) -> "hello"; } }五、学习目标熟悉lambda语法后，主要学习：function、stream。java.util.function、java.util.stream包下接口用法六、Function学习java.util.function包下主要的4中lambda接口用法以及扩展用户1、Function有返回值@FunctionalInterface public interface Function<T, R> { /** * Applies this function to the given argument. * * @param t the function argument * @return the function result */ R apply(T t);范例： //Funcation有返回参数类型 //1、返回Boolean类型 Function<Apple, Boolean> boolearnFunction = apple -> apple.getColor().equals("red"); //2、返回String类型 Function<Apple, String> stringFunction = apple -> apple.getColor(); //3、返回Integer类型 Function<Apple, Integer> integerFunction = apple -> apple.getWeight(); //4、。。。等等其它类型同理2、无返回值@FunctionalInterface public interface Consumer<T> { /** * Performs this operation on the given argument. * * @param t the input argument */ void accept(T t);范例： //Consumer无参数返回类型 Consumer<Apple> appleConsumer = apple -> System.out.println(apple.getColor()); Consumer<Apple> appleConsumer2 = apple -> System.out.println("hello");3、返回Boolean类型@FunctionalInterface public interface Predicate<T> { /** * Evaluates this predicate on the given argument. * * @param t the input argument * @return {@code true} if the input argument matches the predicate, * otherwise {@code false} */ boolean test(T t);范例： //Predicate返回Boolean类型（判断类型） Predicate<Apple> colorPredicate = apple -> apple.getColor().equals("red"); Predicate<Apple> weightPredicate = apple -> apple.getWeight()==4;4、获取对象@FunctionalInterface public interface Supplier<T> { /** * Gets a result. * * @return a result */ T get(); }get(); }  范例： //Supplier获取对象 Supplier<Apple> appleSupplier = Apple::new;根据上面3种接口，返回不同参数类型，在不同地方选择使用。七、那些是FunctionInterface(函数式接口)1、除了default、static的方法外，只有一个方法的接口，就是funcationInteface @FunctionalInterface interface Adder{ int add(int a, int b); }2、没有方法，但继承了有一个方法的接口是funcationInterface @FunctionalInterface interface Empty extends Adder{ }不是函数式接口的1、继承后不止一个方法，因此不是funcationInterface interface SmartAdder extends Adder{ int add(Long a, Long b); }2、没有任何方法的接口，不是funcationInterface interface DoNothing{ }