java8新特新

接口中的默认方法和静态方法

• 接口中可以定义具体方法，但必须“default”修饰
• 接口中可以定义静态方法（系统自动以public 修饰）
• 接口中定义变量（是静态变量，系统自动以public static final修饰）
• 接口和类中方法冲突时，适用“父类优先原则”

package com.test;

public interface TestInterface {
//  public static void eat(){
    static void eat(){

    }

//  public static final double PI = 3.14;
    double PI = 3.14;
    
    default void say(){
        System.out.println("hello world");
    }
}

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函数式接口和Lambda表达式

package com.test;

import java.util.ArrayList;
import java.util.List;

public class App2 {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(3);

        list.forEach(ele -> System.out.println(ele));
        list.forEach(System.out::println);
    }
}

---

Stream API

• 组数操作

  package com.test;
  
  import java.util.Arrays;
  
  public class App3 {
      public static void main(String[] args) {
          String[] strArr = {"hello","world","hadoop","spark","yarn","storm"};
          long count = Arrays.stream(strArr).filter(ele -> ele.length() == 5).count();
          System.out.println(count);
      }
  }
  

• 集合操作

package com.test;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class App3 {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(3);
        List<Integer> newList = list.stream().map(ele -> ele * ele).collect(Collectors.toList());
        newList.forEach(ele -> System.out.println(ele));

    }
}

• 并行操作

package com.test;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class App3 {
    public static void main(String[] args) {
        List<Integer> list = new ArrayList<>();
        list.add(1);
        list.add(2);
        list.add(3);
        List<Integer> newList = list.parallelStream().map(ele -> ele * ele).collect(Collectors.toList());
        newList.forEach(ele -> System.out.println(ele));
    }
}

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日期操作

https://blog.youkuaiyun.com/qq_27093465/article/details/78909797