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java.util.function包中有43个function interface，然而实际上只有四大类：
Consumers消费者
Supplier供应商
Functions性能
Predicates谓词
1.Consumers一个对象，BiConsumer两个对象
理论都是对传入的T实体进行操作解决
public interface Consumer<T> { public void accept(T var1);}Consumer<String> printer = s-> System.out.println(s);//或者Consumer<String> printer = System.out::println;public interface BiConsumer<T, U> { void accept(T var1, U var2);}2.Supplier返回类型T的对象，没有任何入参
理论是创立了T实体并返回的操作
public interface Supplier<T> { T get();}Supplier<BankAccount> bankAccountSupplier = ()->new BankAccount();//或者Supplier<BankAccount> bankAccountSupplier = BankAccount::new;3.Function
实际上是对类型T实体进行相应的操作并返回类型为R的实体
public interface Function<T, R> { R apply(T var1);}Function<BankAccount, Integer> amtFunction = bankAccount -> bankAccount.getBalance();//或者Function<BankAccount, Integer> amtFunction = BankAccount::getBalance;4.Predicate
确定实体T是否满足束缚，返回boolean
public interface Predicate<T> { boolean test(T t);}Predicate<BankAccount> test = bankAccount -> bankAccount.getBalance()>10;//自定义Predicate<String> p = new Predicate<String>() { @Override public boolean test(String s) { return s.length()<20; }};p = s -> s.length()<20;System.out.println(p.test("Hello 12321321321321312321321"));5.还有一些其余的类型
intPredicate，intFunction，intConsumer，入参须要指定为int
以及intToDoubleFunction，入参为int，返回参数为double
public interface IntFunction<R> { R apply(int value);}public interface LongToDoubleFunction { double applyAsDouble(long value);}能够自定义Predicate接口，规范验证以及自定义办法，静态方法等
@FunctionalInterfacepublic interface Predicate<T> { public boolean test(T t); public default Predicate<T> and(Predicate<T> other){ return t -> test(t) && other.test(t); } public default Predicate<T> or(Predicate<T> other){ return t -> test(t) || other.test(t); } //静态方法第一种 public static Predicate<String> isEqualsTo(String string){ return s -> s.equals(string); } //还能够写成另一种 public static <U> Predicate<U> isEqualsTo(U u){ return s -> s.equals(u); }}public class Main { public static void main(String[] args) { Predicate<String> p1 = s -> s.length()<20; Predicate<String> p2 = s -> s.length()>5; boolean b= p1.test("Hello"); System.out.println("Hello is shorter than 20 chars is :"+b);输入：Hello is shorter than 20 chars is :true Predicate<String> p3 = p1.and(p2); System.out.println("p3 test 123 :"+p3.test("123")); System.out.println("p3 test 123456 :"+p3.test("123456")); System.out.println("p3 test 123456789012345678901 :"+p3.test("123456789012345678901"));输入：p3 test 123 :falsep3 test 123456 :truep3 test 123456789012345678901 :false Predicate<String> p4 = p1.or(p2); System.out.println("p4 test 123 :"+p4.test("123")); System.out.println("p4 test 123456 :"+p4.test("123456")); System.out.println("p4 test 123456789012345678901 :"+p4.test("123456789012345678901"));输入：p4 test 123 :truep4 test 123456 :truep4 test 123456789012345678901 :true Predicate<String> p5 = Predicate.isEqualsTo("YES"); System.out.println("p5 test YES :"+p5.test("YES")); System.out.println("p5 test NO :"+p5.test("NO"));输入：p5 test YES :truep5 test NO :false }}