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!");
    }
}

package cn.intcast.demo17;

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

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!");
    }
}

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