JAVA进阶22

1、接口默认方法的使用

①接口的默认方法可以通过接口实现类对象直接调用。

②接口的默认方法也可以被接口实现类进行覆盖重写

 package cn.intcast.demo17;

 public interface MyInterfaceDefault {
     //抽象方法
     public abstract void methodAbs();
 //    void AAA();
     public default void methodA(){
         System.out.println("this is a default method!");
     }
 }

接口类1

 package cn.intcast.demo17;

 public class MyInterfaceDefaultA implements MyInterfaceDefault {
     @Override
     public void methodAbs() {
         System.out.println("实现了抽象 方法，AAA；");
     }
 }

接口实现类

 package cn.intcast.demo17;

 public class Code01Interface {
     public static void main(String[] args) {
         //创建实现类对象
         MyInterfaceDefaultA s = new MyInterfaceDefaultA();
         //调用抽象方法，如果实现类当中没有，会向上找接口
         s.methodA();
         s.methodAbs();
     }
 }

运行结果图

2、接口的静态方法使用

接口中的静态方法可以通过接口名称，调用其中的静态方法

格式：接口名称.静态方法名（参数）

 package cn.intcast.demo17;

 public interface StaticInterface {
     public static void staticmethod(){
         System.out.println("this is a static method!");
     }
 }

静态方法

 package cn.intcast.demo17;

 public class CodeStatic {
     public static void main(String[] args) {
         StaticInterface.staticmethod();
     }
 }

运行结果图

3、Collections工具类

 package cn.demo01;

 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;

 public class Test03 {
     public static void main(String[] args){
         List<String> aList = new ArrayList<>();
         for (int i = 0; i < 5; i++) {
             aList.add("a"+i);
         }
         System.out.println(aList);
         //随机排查
         Collections.shuffle(aList);
         System.out.println(aList);
         //逆序
         Collections.reverse(aList);
         System.out.println(aList);
         //顺序
         Collections.sort(aList);
         System.out.println(aList);
         System.out.println(Collections.binarySearch(aList,"a2"));
         Collections.fill(aList,"hello");
         System.out.println(aList);
         }
     }

运行结果图

4、ORM思想的简单实验：map表示一行数据，多行数据是多个map；将多个map放到list中（存放表格数据）

 package cn.demo01;

 import java.util.*;

 public class TestTableDate01 {
     public static void main(String[] args) {
         Map<String,Object> row1 = new HashMap<>();
         row1.put("id",101);
         row1.put("姓名","张一");
         row1.put("age",18);

         Map<String,Object> row2 = new HashMap<>();
         row2.put("id",102);
         row2.put("姓名","张二");
         row2.put("age",22);

         List<Map<String,Object>> table1 = new ArrayList<>();
         table1.add(row1);
         table1.add(row2);

         for (Map<String,Object> row:table1){
             Set<String> keyset = row.keySet();
             for (String key:keyset){
                 System.out.print(key+":"+row.get(key)+"\t");
             }
             System.out.println();
         }
     }
 }

运行结果图

5、表格数据的存储

 package cn.demo01;

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

 public class TestTableDate02 {
     public static void main(String[] args) {
         User u1 = new User(101,"王大",20,88);
         User u2 = new User(102,"王二",23,85);
         User u3 = new User(103,"王三",20,84);

         List<User> list = new ArrayList<>();
         list.add(u1);
         list.add(u2);
         list.add(u3);

         for (User u:list){
             System.out.println(u);
         }
     }
 }

 class User{
     private int id;
     private String name;
     private int age;
     private double grade;

     public User() {
     }

     public User(int id, String name, int age, double grade) {
         this.id = id;
         this.name = name;
         this.age = age;
         this.grade = grade;
     }

     public int getId() {
         return id;
     }

     public void setId(int id) {
         this.id = id;
     }

     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 getGrade() {
         return grade;
     }

     public void setGrade(double grade) {
         this.grade = grade;
     }

     public String toString(){
         return "id:"+id+"\t"+"name:"+name+"\t"+"grade:"+grade+"\t"+"age:"+age+"\t";
     }
 }

运行结果图