目的
有一种场景 比如我们需要根据特定的条件 从集合里面 获取符合特定条件的记录 过滤记录 ； lambda 为我们提供了更好的机制
当然我们可以采用filter , 但是这个地方更多的是想要使用一些接口函数；
Consumer Function Predicate Supplier;
名称 参数 返回值 实例
Consumer 有 无 Iterable上的forEach方法
Function 有 有 Optional的map方法
Predicate 有 有(bool) Optional的filter方法
Supplier 无 有 懒加载、惰性求值、Stream的generate(静态)
public class Demo {
public static void main(String[] args) {
new Demo().show(2, () -> {
return "lambda interface call";
});
//Supplier get 来做生产
int[] arr = {90, 2, 77, -1, 100};
int max = getMax(() -> {
int temp = 0;
for (int e : arr) {
if (e > temp) {
temp = e;
}
}
return temp;
});
System.out.println("max element : " + max);
//Consumer 消费
consum("java", (name) -> {
System.out.println(new StringBuilder(name).reverse());
});
//分别指向2个方法 name为原始的入参 java
consums("java", (name) -> {
System.out.println(name + "111111111111111");
}, (name) -> {
System.out.println(name + "2222222222222");
});
//Predict 来bool判断
boolean checkString = checkString("java", (str) -> {
return str.length() > 5;
});
System.out.println(checkString);
//Function
changeType("12",(s)->{
return Integer.valueOf(s);
});
//第一次将字符串12 转为了12整数 ，然后将12整数和java doc进行拼接
changeTypes("12",(s)->{
return Integer.valueOf(s);
},(s)->{
//integer
System.out.println(s.getClass().getName());
return s + "java doc";
});
}
public static void changeType(String s , Function<String,Integer> function){
int in = function.apply(s);
System.out.println(in);
}
public static void changeTypes(String s , Function<String,Integer> function, Function<Integer,String> function2){
String in = function.andThen(function2).apply(s);
System.out.println(in);
}
public static boolean checkString(String s, Predicate<String> predict) {
return predict.test(s);
}
public static void consum(String name, Consumer<String> consumer) {
consumer.accept(name);
}
public static void consums(String name, Consumer<String> consumer, Consumer<String> consumer2) {
consumer.andThen(consumer2).accept(name);
}
public static int getMax(Supplier<Integer> supplier) {
return supplier.get();
}
public void show(int level, MessageBuilder messageBuilder) {
System.out.println(level + " -- " + messageBuilder.buildMessage());
}
}
对条件的过滤
public class PredicateDemo {
public static void main(String[] args) {
//获取age>25的学生集合
System.out.println(getTargetList(Student.list, (s) -> {
return s.getAge() > 25;
}));
//获取age>25 或者 名字包含 java 的学生集合
System.out.println(getTargetListOr(Student.list, (s) -> {
return s.getAge() > 25;
}, (s) -> {
return s.getName().contains("java");
}));
//获取age>25 并且 名字包含 java 的学生集合
//获取age>=25岁的学生
System.out.println(getTargetListNagtive(Student.list, (s) -> {
return s.getAge() < 25;
}));
}
public static List<Student> getTargetList(List<Student> list, Predicate<Student> predicate) {
List<Student> result = new ArrayList<>();
for (Student s : list) {
if (predicate.test(s)) {
result.add(s);
}
}
return result;
}
public static List<Student> getTargetListNagtive(List<Student> list, Predicate<Student> predicate) {
List<Student> result = new ArrayList<>();
for (Student s : list) {
if (predicate.negate().test(s)) {
result.add(s);
}
}
return result;
}
public static List<Student> getTargetListOr(List<Student> list, Predicate<Student> predicate, Predicate<Student> predicate2) {
List<Student> result = new ArrayList<>();
for (Student s : list) {
if (predicate.or(predicate2).test(s)) {
result.add(s);
}
}
return result;
}
public static List<Student> getTargetListAnd(List<Student> list, Predicate<Student> predicate, Predicate<Student> predicate2) {
List<Student> result = new ArrayList<>();
for (Student s : list) {
if (predicate.and(predicate2).test(s)) {
result.add(s);
}
}
return result;
}
}
public class Student {
private int age;
private String name;
static List<Student> list = new ArrayList<Student>() ;
public Student() {
}
public Student(int age, String name) {
this.age = age;
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public String toString() {
return "Student{" +
"age=" + age +
", name='" + name + '\'' +
'}';
}
}