一文带你入门JDK8新特性——Lambda表达式

/**多参数无返回*/
@FunctionalInterface
public interface NoReturnMultiParam {
 void method(int a, int b);
}

/**无参无返回值*/
@FunctionalInterface
public interface NoReturnNoParam {
 void method();
}

/**一个参数无返回*/
@FunctionalInterface
public interface NoReturnOneParam {
 void method(int a);
}

/**多个参数有返回值*/
@FunctionalInterface
public interface ReturnMultiParam {
 int method(int a, int b);
}

/*** 无参有返回*/
@FunctionalInterface
public interface ReturnNoParam {
 int method();
}

/**一个参数有返回值*/
@FunctionalInterface
public interface ReturnOneParam {
 int method(int a);
}

import lambda.interfaces.*;

public class Test1 {
 public static void main(String[] args) {

  //无参无返回
  NoReturnNoParam noReturnNoParam = () -> {
   System.out.println("NoReturnNoParam");
  };
  noReturnNoParam.method();

  //一个参数无返回
  NoReturnOneParam noReturnOneParam = (int a) -> {
   System.out.println("NoReturnOneParam param:" + a);
  };
  noReturnOneParam.method(6);

  //多个参数无返回
  NoReturnMultiParam noReturnMultiParam = (int a, int b) -> {
   System.out.println("NoReturnMultiParam param:" + "{" + a +"," + + b +"}");
  };
  noReturnMultiParam.method(6, 8);

  //无参有返回值
  ReturnNoParam returnNoParam = () -> {
   System.out.print("ReturnNoParam");
   return 1;
  };

  int res = returnNoParam.method();
  System.out.println("return:" + res);

  //一个参数有返回值
  ReturnOneParam returnOneParam = (int a) -> {
   System.out.println("ReturnOneParam param:" + a);
   return 1;
  };

  int res2 = returnOneParam.method(6);
  System.out.println("return:" + res2);

  //多个参数有返回值
  ReturnMultiParam returnMultiParam = (int a, int b) -> {
   System.out.println("ReturnMultiParam param:" + "{" + a + "," + b +"}");
   return 1;
  };

  int res3 = returnMultiParam.method(6, 8);
  System.out.println("return:" + res3);
 }
}

import lambda.interfaces.*;

public class Test2 {
 public static void main(String[] args) {

  //1.简化参数类型，可以不写参数类型，但是必须所有参数都不写
  NoReturnMultiParam lamdba1 = (a, b) -> {
   System.out.println("简化参数类型");
  };
  lamdba1.method(1, 2);

  //2.简化参数小括号，如果只有一个参数则可以省略参数小括号
  NoReturnOneParam lambda2 = a -> {
   System.out.println("简化参数小括号");
  };
  lambda2.method(1);

  //3.简化方法体大括号，如果方法条只有一条语句，则可以胜率方法体大括号
  NoReturnNoParam lambda3 = () -> System.out.println("简化方法体大括号");
  lambda3.method();

  //4.如果方法体只有一条语句，并且是 return 语句，则可以省略方法体大括号
  ReturnOneParam lambda4 = a -> a+3;
  System.out.println(lambda4.method(5));

  ReturnMultiParam lambda5 = (a, b) -> a+b;
  System.out.println(lambda5.method(1, 1));
 }
}

public class Exe1 {
 public static void main(String[] args) {
  ReturnOneParam lambda1 = a -> doubleNum(a);
  System.out.println(lambda1.method(3));

  //lambda2 引用了已经实现的 doubleNum 方法
  ReturnOneParam lambda2 = Exe1::doubleNum;
  System.out.println(lambda2.method(3));

  Exe1 exe = new Exe1();

  //lambda4 引用了已经实现的 addTwo 方法
  ReturnOneParam lambda4 = exe::addTwo;
  System.out.println(lambda4.method(2));
 }

 /**
  * 要求
  * 1.参数数量和类型要与接口中定义的一致
  * 2.返回值类型要与接口中定义的一致
  */
 public static int doubleNum(int a) {
  return a * 2;
 }

 public int addTwo(int a) {
  return a + 2;
 }
}

interface ItemCreatorBlankConstruct {
 Item getItem();
}
interface ItemCreatorParamContruct {
 Item getItem(int id, String name, double price);
}

public class Exe2 {
 public static void main(String[] args) {
  ItemCreatorBlankConstruct creator = () -> new Item();
  Item item = creator.getItem();

  ItemCreatorBlankConstruct creator2 = Item::new;
  Item item2 = creator2.getItem();

  ItemCreatorParamContruct creator3 = Item::new;
  Item item3 = creator3.getItem(112, "鼠标", 135.99);
 }
}

 Thread t = new Thread(() -> {
  for (int i = 0; i < 10; i++) {
  System.out.println(2 + ":" + i);
  }
 });
  t.start();

 @FunctionalInterface
 public interface Consumer<T> {
  void accept(T t);
  //....
 }
  ArrayList<Integer> list = new ArrayList<>();

  Collections.addAll(list, 1,2,3,4,5);

  //lambda表达式 方法引用
  list.forEach(System.out::println);

  list.forEach(element -> {
  if (element % 2 == 0) {
   System.out.println(element);
  }
  });

  ArrayList<Item> items = new ArrayList<>();
  items.add(new Item(11, "小牙刷", 12.05 ));
  items.add(new Item(5, "日本马桶盖", 999.05 ));
  items.add(new Item(7, "格力空调", 888.88 ));
  items.add(new Item(17, "肥皂", 2.00 ));
  items.add(new Item(9, "冰箱", 4200.00 ));

  items.removeIf(ele -> ele.getId() == 7);

  //通过 foreach 遍历，查看是否已经删除
  items.forEach(System.out::println);

  ArrayList<Item> list = new ArrayList<>();
  list.add(new Item(13, "背心", 7.80));
  list.add(new Item(11, "半袖", 37.80));
  list.add(new Item(14, "风衣", 139.80));
  list.add(new Item(12, "秋裤", 55.33));

  /*
  list.sort(new Comparator<Item>() {
   @Override
   public int compare(Item o1, Item o2) {
    return o1.getId() - o2.getId();
   }
  });
  */

  list.sort((o1, o2) -> o1.getId() - o2.getId());

  System.out.println(list);