定义函数式接口时,@FunctionalInterface可选,就算不写,只要保证满足函数式接口定义条件,也照样是函数式接口(建议加上该注解)。
需求:
public class Demo {
public static void main(String[] args) {
startThread(() -> System.out.println(Thread.currentThread().getName()+"线程启动了"));
}
private static void startThread(Runnable r){
new Thread(r).start();
}
}
如果方法的参数是一个函数式接口,可以使用Lambda表达式作为参数传递
需求:
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class Demo {
public static void main(String[] args) {
ArrayList<String> a = new ArrayList<>();
a.add("cc");
a.add("aaaaa");
a.add("bbb");
Collections.sort(a,getCommparator());
System.out.println(a);
}
private static Comparator<String> getCommparator(){
//方法1
// Comparator<String> c = new Comparator<String>() {
// @Override
// public int compare(String s, String t1) {
// return s.length() - t1.length();
// }
// };
// return c;
//方法2
// return new Comparator<String>() {
// @Override
// public int compare(String s, String t1) {
// return s.length() - t1.length();
// }
// }
//方法3
return ( s1, s2) -> s1.length() -s2.length();
}
}
如果方法的返回值式一个函数式接口,我们可以使用Lambda表达式结果返回
java 8在java.util.function包下预定义了大量的函数式接口
如:
import java.util.function.Supplier;
public class Demo {
public static void main(String[] args) {
String s = getString(() -> "Hello,World");
System.out.println(s);
Integer i = getIneger(() -> 5);
System.out.println(i);
}
private static int getIneger(Supplier<Integer> s) {
return s.get();
}
private static String getString(Supplier<String> s) {
return s.get();
}
}
import java.util.Arrays;
import java.util.function.Supplier;
public class SupplierTest {
public static void main(String[] args) {
int[] i = {1, 2, 3, 52, 68, 45};
int IntegerMax = getMax(() -> {
Arrays.sort(i);
return i[i.length - 1];
}
);
System.out.println(IntegerMax);
}
private static int getMax(Supplier<Integer> s) {
return s.get();
}
}
import java.util.function.Consumer;
public class ConsumerDemo {
public static void main(String[] args) {
//Lambda表达式
operatorString("Hello,World",s-> System.out.println(s));
//方法引用
operatorString("Hello,World",System.out::println);
}
private static void operatorString(String n, Consumer<String> c){
c.accept(n);
}
}
import java.util.function.Consumer;
public class ConsumerTest {
public static void main(String[] args) {
String [] strArray = {"张三,18","李四,20","王五,19"};
// operatorConsumer(strArray,s -> {
// String name = s.split(",")[0];
// System.out.print("姓名:"+name);
// },s -> {
// int age = Integer.parseInt(s.split(",")[1]);
// System.out.println(",年龄:"+age);
// });
operatorConsumer(strArray,
s -> System.out.print("姓名:"+s.split(",")[0]),
s -> System.out.println(",年龄:"+Integer.parseInt(s.split(",")[1])));
}
private static void operatorConsumer(String [] strArray, Consumer<String> c1, Consumer<String> c2){
for (String i:strArray){
c1.andThen(c2).accept(i);
}
}
}
test方法与negate方法:
import java.util.function.Predicate;
public class PredicateDemo {
public static void main(String[] args) {
boolean b1 = checkString("hello", s -> s.length() > 8);
System.out.println(b1);
boolean b2 = checkString("hello", s -> s.length() < 8);
}
//判断给定字符串是否满足要求
private static boolean checkString(String s, Predicate<String> p) {
// return p.test(s);
// return !p.test(s);
return p.negate().test(s);
}
}
and方法与or方法:
import java.util.function.Predicate;
public class PredicateDemo2 {
public static void main(String[] args) {
boolean b1 = checkString("hello", s -> s.length() > 8);
System.out.println(b1);
boolean b2 = checkString("hello", s -> s.length() < 8);
System.out.println(b2);
boolean b3 = checkString("hello", s -> s.length() > 8, s -> s.length() < 8);
System.out.println(b3);
}
//判断给定字符串是否满足要求
private static boolean checkString(String s, Predicate<String> p) {
return p.test(s);
}
//同一个字符串给出两个不同的判断条件,最后把这两个判断条件结果做逻辑与运算的结果作为最终的结果
private static boolean checkString(String s, Predicate<String> p, Predicate<String> p2) {
// return p.and(p).and(p2).test(s); //false
return p.or(p).or(p2).test(s); //true
}
}
import java.util.ArrayList;
import java.util.function.Predicate;
public class PredicateTest {
public static void main(String[] args) {
String[] strArray = {"张三,18", "李四,20", "王五,19", "王麻子,21", "张三丰,17"};
ArrayList<String> array = myFilter(strArray,
s -> s.split(",")[0].length() > 2,
s -> Integer.parseInt(s.split(",")[1]) > 19);
for (String i : array){
System.out.println(i);
}
}
private static ArrayList<String> myFilter(String[] strArray, Predicate<String> p1, Predicate<String> p2) {
ArrayList<String> array = new ArrayList<>();
for (String i : strArray) {
if (p1.and(p2).test(i)) {
array.add(i);
}
}
return array;
}
}
常用方法:
import java.util.function.Function;
public class Demo {
public static void main(String[] args) {
Convert("50", s -> Integer.parseInt(s));
Convert("100", Integer::parseInt);
Convert(100, i -> String.valueOf(i + 20));
Convert("66", s -> Integer.parseInt(s), i -> String.valueOf(i+30));
}
//定义一个方法,把一个字符串转换int类型,控制台输出
private static void Convert(String s, Function<String, Integer> fun) {
int apply = fun.apply(s);
System.out.println(apply);
}
//定义一个方法,把一个int类型的数据加上一个整数之后,转为字符串在控制台输出
private static void Convert(int i, Function<Integer, String> fun) {
String s = fun.apply(i);
System.out.println(s);
}
//定义一个方法,把一个字符串转换int类型,把int类型的数据加上一个整数之后,
// 转换字符串在控制台输出
private static void Convert(String s, Function<String, Integer> fun1, Function<Integer, String> fun2) {
// Integer i = fun1.apply(s);
// String ss = fun2.apply(i);
// System.out.println(ss);
String ss = fun1.andThen(fun2).apply(s);
System.out.println(ss);
}
}
import java.util.function.Function;
public class Demo {
public static void main(String[] args) {
Convert("张三,20",s -> s.split(",")[1],s -> Integer.parseInt(s),i -> (i+10));
}
private static void Convert(String s, Function<String,String> fun1,Function<String,Integer> fun2,Function<Integer,Integer> fun3){
int i = fun1.andThen(fun2).andThen(fun3).apply(s);
System.out.println(i);
}
}
原文:https://www.cnblogs.com/Hz-z/p/13086999.html