2.面向对象

1.1.类的定义

创建类

package derek.day06.demo;

public class Student {
    //成员变量
    String name;
    int age;

    //成员方法
    public void eat(){
        System.out.println("吃饭");
    }
    public void study(){
        System.out.println("学习");
    }

}

创建对象

package derek.day06.demo;

public class demoStudent {
    public static void main(String[] args) {
        //创建对象
        Student stu = new Student();
        stu.name = "derek";
        stu.age = 18;
        System.out.println(stu.name);
        stu.eat();
    }
}

1.2.private关键字

package derek.day06.demo;

public class Student {
    //成员变量
    String name;
    private int age;

    public void show(){
        System.out.println(name+":"+age);
    }

    public void setAge(int num){
        if (num < 100 && num > 0){
            age = num;
        }else {
            System.out.println("错误的数据");
        }

    }

    public int getAge(){
        return age;
    }

}

package derek.day06.demo;

public class demoStudent {
    public static void main(String[] args) {
        Student stu = new Student();

        stu.name = "derek";
        stu.setAge(18);
        stu.show();
    }
}

1.3.构造方法

package derek.day06.demo;

import org.w3c.dom.ls.LSOutput;

public class Student {
    //成员变量
    private String name;
    private int age;

    //无参数的构造方法
    public Student(){
        System.out.println("无参数的构造方法执行");
    }

    //全参数的构造方法
    public Student(String name, int age){
        System.out.println("全参构造方法执行");
        this.name = name;
        this.age = age;
    }

    public void setName(String name){
        this.name = name;
    }

    public String getName(){
        return name;
    }

    public void setAge(int age){
        this.age = age;
    }

    public int getAge(){
        return age;
    }

}

package derek.day06.demo;

public class demoStudent {
    public static void main(String[] args) {
        Student s1 = new Student();    //无参数的构造方法执行

        Student s2 = new Student("derek", 18);   //全参构造方法执行
    }
}

1.4.Scanner类

package derek.learn;

//1.导包
import java.util.Scanner;

public class DemoScanner {
    public static void main(String[] args) {
        //2.创建，System.in代表从键盘进行输入
        Scanner sc = new Scanner(System.in);
        //3.使用,获取键盘输入的int数字
        int num = sc.nextInt();
        System.out.println(num);
        //字符串
        String name = sc.next();
        System.out.println(name);
    }
}

1.5.Random类

package derek.learn;

import java.util.Random;

public class DemoRandom {
    public static void main(String[] args) {
        Random r = new Random();
        int num = r.nextInt(10);
        System.out.println(num);
    }
}

1.6.ArrayList集合

package derek.learn;

import java.util.ArrayList;

public class DemoArrayList {
    public static void main(String[] args) {
        //创建一个ArrayList集合，里面是String类型的数据
        ArrayList<String> list = new ArrayList<>();
        System.out.println(list);   //[]

        //1.向集合中添加数据
        list.add("迪丽热巴");
        list.add("古力娜扎");
        list.add("马尔扎哈");
        System.out.println(list);    //[迪丽热巴, 古力娜扎, 马尔扎哈]

        //2.获取
        System.out.println(list.get(1));     //古力娜扎

        //3.删除
        list.remove(1);
        System.out.println(list);    //[迪丽热巴, 马尔扎哈]

        //4.获取集合长度
        System.out.println(list.size());    //2

        //5.遍历
        for (int i = 0; i < list.size(); i++) {
            System.out.println(list.get(i));
        }
    }
}

1.7.String类

package derek.learn;

public class DemoString {
    public static void main(String[] args) {
        String str1 = "Zhang";
        String str2 = "Derek";
        //1.拼接字符串
        String str3 = str1.concat(str2);
        System.out.println(str3);    //ZhangDerek

        //2.获取指定索引位置的字符
        System.out.println(str1.charAt(1));   //h

        //3.获取子字符串的索引
        System.out.println(str3.indexOf('e'));    //6

        //4.截取
        System.out.println(str3.substring(1,4));   //han

        //5.转换成为字符数组
        char[] chars = "Hello".toCharArray();
        System.out.println(chars[1]);   //e

        //6.替换
        String str4 = "aaabbbccc";
        String str5 = str4.replace('a','d');
        System.out.println(str5);     //dddbbbccc

        //7.分割
        String str6 = "aa,bb,cc,d";
        String[] arr = str6.split(",");
        System.out.println(arr[1]);    //bb
    }
}