Java进阶13讲__第五讲

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JDK8新特性-Lambda

1.认识Lambda 

 2.Lambda表达式的省略写法

进一步简化Lambda表达式的写法

 

package cn.hdc.oop5.lambda;import java.util.Arrays;
import java.util.Comparator;public class Test2 {public static void main(String[] args) {double[] price = {99.8, 128, 100};
//        Arrays.setAll(price, (int value) -> {
//            return price[value] * 0.8;
//        });/*** 参数类型可以省略不写* 如果只有一个参数，参数类型可以省略同时()也可以省略*/
//        Arrays.setAll(price, value -> {
//            return price[value] * 0.8;
//        });/*** 如果Lambda表达式中的方法体代码只有一行代码，可以省略大括号不写，同时要省略分号!此时，如* 果这行代码是return语句，也必须去掉return不写，*/Arrays.setAll(price, value -> price[value] * 0.8);System.out.println("-------------------------------------------------------");Student[] students = new Student[4];students[0] = new Student("蜘蛛精", 169.5, 23);students[1] = new Student("紫霞", 163.8, 26);students[2] = new Student("紫霞", 163.8, 26);students[3] = new Student("至尊宝", 167.5, 24);
//        Arrays.sort(students, new Comparator<Student>() {
//            @Override
//            public int compare(Student o1, Student o2) {
//                return (int) (o1.getHeight() - o2.getHeight());
//            }
//        });
//        Arrays.sort(students, (Student o1, Student o2) -> {
//            return Double.compare(o1.getHeight(), o2.getHeight());
//        });
//        Arrays.sort(students, (o1, o2) -> {
//            return Double.compare(o1.getHeight(), o2.getHeight());
//        });Arrays.sort(students, (o1, o2) -> Double.compare(o1.getHeight(), o2.getHeight()));}
}class Student {private String name;private double height;private int age;public String getName() {return name;}public void setName(String name) {this.name = name;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public double getHeight() {return height;}public void setHeight(double height) {this.height = height;}public Student(String name, double height, int age) {this.name = name;this.height = height;this.age = age;}@Overridepublic String toString() {return "Student{" +"name='" + name + '\'' +", height=" + height +", age=" + age +'}';}
}

3.方法引用

Lambda表达式用来简化函数式接口的匿名内部类
方法引用进一步简化Lambda表达式
方法引用的标志性符号：“ :: ”

1.静态方法的引用

package cn.hdc.oop5.staticMethod;import cn.hdc.oop5.lambda.Student;import java.util.Arrays;
import java.util.Comparator;public class Test {public static void main(String[] args) {Student[] students = new Student[4];students[0] = new Student("蜘蛛精", 169.5, 23);students[1] = new Student("紫霞", 163.8, 26);students[2] = new Student("紫霞", 163.8, 26);students[3] = new Student("至尊宝", 167.5, 24);Arrays.sort(students, (o1, o2) -> o1.getAge() - o2.getAge());Arrays.sort(students, (o1, o2) -> CompareByData.compareByAge(o1, o2));/*** 如果某个Lambda表达式里只是调用一个静态方法，并且前后参数的形式一致，就可以使用静态方法引用。*/Arrays.sort(students, CompareByData::compareByAge);}
}

package cn.hdc.oop5.staticMethod;import cn.hdc.oop5.lambda.Student;public class CompareByData {public static int compareByAge(Student s1, Student s2) {return s1.getAge() - s2.getAge();}
}

2.实例方法的引用

 

package cn.hdc.oop5.staticMethod;import cn.hdc.oop5.lambda.Student;import java.util.Arrays;
import java.util.Comparator;public class Test {public static void main(String[] args) {Student[] students = new Student[4];students[0] = new Student("蜘蛛精", 169.5, 23);students[1] = new Student("紫霞", 163.8, 26);students[2] = new Student("紫霞", 163.8, 26);students[3] = new Student("至尊宝", 167.5, 24);Arrays.sort(students, (o1, o2) -> new CompareByData().compareByHeight(o1, o2));/*** 如果某个Lambda表达式里只是调用一个实例方法，并且前后参数的形式一致，就可以使用实例方法引用*/Arrays.sort(students, new CompareByData()::compareByHeight);}
}

package cn.hdc.oop5.staticMethod;import cn.hdc.oop5.lambda.Student;public class CompareByData {public int compareByHeight(Student s1, Student s2) {return (int) (s1.getHeight() - s2.getHeight());}
}

3.特定类型方法的引用

package cn.hdc.oop5.special;import java.util.Arrays;
import java.util.Comparator;public class specialImport {public static void main(String[] args) {String[] names = {"boby", "angela", "Andy", "dlei", "caocao", "Babo", "jack", "Cici"};
//        Arrays.sort(names);
//        Arrays.sort(names, new Comparator<String>() {
//            @Override
//            public int compare(String o1, String o2) {
//                return o1.compareToIgnoreCase(o2);
//            }
//        });
//        Arrays.sort(names, (o1, o2) -> o1.compareToIgnoreCase(o2));/*** 如果某个Lambda表达式里只是调用一个实例方法，* 并且前面参数列表中的第一个参数是作为方法的主调* 后面的所有参数都是作为该实例方法的入参的，则此时就可以使用特定类型的方法引用。*/Arrays.sort(names, String::compareToIgnoreCase);System.out.println(Arrays.toString(names));}
}

4.构造器的引用

package cn.hdc.oop5.constructor;public class constructorImport {public static void main(String[] args) {
//        CreateCar cc = new CreateCar() {
//            @Override
//            public Car create(String name, double price) {
//                return new Car(name, price);
//            }
//        };
//        CreateCar cc = (name, price) -> new Car(name, price);/*** 如果某个Lambda表达式里只是在创建对象，并且前后参数情况一致，就可以使用构造器引用*/CreateCar cc = Car::new;//构造器引用Car C = cc.create("BMW", 49.9);System.out.println(C);}
}interface CreateCar {Car create(String name, double price);
}

package cn.hdc.oop5.constructor;public class Car {private String name;private double price;@Overridepublic String toString() {return "Car{" +"name='" + name + '\'' +", price=" + price +'}';}public Car() {}public Car(String name, double price) {this.name = name;this.price = price;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}
}

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