Introduction to the

Boolean valued function

Look at the source code

Elements of perceived

  • The return value isboolean
  • There are abstract methodstest
  • And not and not (And, negate, or) default method method,Implies that two Predicate objects can be used together
  • If you understand BiFunction, it’s easy to understand Predicate

test

public class PredicateTest {
    public static void main(String[] args) {
        PredicateTest test = new PredicateTest();
        List<Integer> list = Arrays.asList(1.2.3.4.5.6.7.8.9.10);
        test.printByCondition(list,l -> l%2= =0);/ / print even
        System.out.println("\n"+"-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --");
        test.printByConditionNegate(list,l -> l%2= =0);   / / print is not even
        System.out.println("\n"+"-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --");
        test.printByConditionAnd(list,l -> l%2= =0,l -> l>4);  //print even numbers greater than 4
        System.out.println("\n"+"-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --");
        test.printByConditionOr(list,l -> l%2= =0,l -> l<4);  Print even numbers or numbers less than 4
    }
    public void printByCondition(List<Integer> list, Predicate<Integer> predicate){
        //l indicates an element in the list. // An element is output if it meets certain criteria
        list.forEach( l -> { if (predicate.test(l))  System.out.print(l+""); });
    }
    public void printByConditionNegate(List<Integer> list, Predicate<Integer> predicate){
        //l indicates an element in the list. // An element does not meet certain criteria
        list.forEach( l -> { if (predicate.negate().test(l))  System.out.print(l+""); });
    }
    public void printByConditionAnd(List<Integer> list, Predicate<Integer> predicate1,Predicate<Integer> predicate2){
                              // An element satisfies both conditions
        list.forEach( l -> { if (predicate1.and(predicate2).test(l))  System.out.print(l+""); });
    }
    public void printByConditionOr(List<Integer> list, Predicate<Integer> predicate1,Predicate<Integer> predicate2){
                              // An element satisfies a condition
        list.forEach( l -> { if (predicate1.or(predicate2).test(l))  System.out.print(l+""); }); }}Copy the code

explain

  • It is important to always keep in mind the meaning of a Lambda expression, that is, an abstract method in the implementation interface that will eventually be usedInterFaceClass.method
  • Both arguments and return values are indispensable

summary

Function of Lambda expressions

  • Transfer behavior, not just values
  • Raising the level of abstraction 
    • public void printByCondition(List<Integer> list, Predicate<Integer> predicate){
    //l indicates an element in the list. // An element is output if it meets certain criteria
    list.forEach( l -> { if (predicate.test(l))  System.out.print(l+""); });
}
Copy the code
    • Look at this method alone, it only knows that if it satisfies some condition, but it doesn’t know exactly what condition, so it raises the level of abstraction. Right
  • Apis are more reusable
  • More flexible
    • The same method can be replaced with lambda expressions at will, so it is more reusable and flexible