2.面向對象

1.1.類的定義

創建類

package derek.day06.demo;

public class Student {
    //成員變數
    String name;
    int age;

    //成員方法
    public void eat(){
        System.out.println("吃飯");
    }
    public void study(){
        System.out.println("學習");
    }

}

創建對象

package derek.day06.demo;

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

1.2.private關鍵字

package derek.day06.demo;

public class Student {
    //成員變數
    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("錯誤的數據");
        }

    }

    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.構造方法

package derek.day06.demo;

import org.w3c.dom.ls.LSOutput;

public class Student {
    //成員變數
    private String name;
    private int age;

    //無參數的構造方法
    public Student(){
        System.out.println("無參數的構造方法執行");
    }

    //全參數的構造方法
    public Student(String name, int age){
        System.out.println("全參構造方法執行");
        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();    //無參數的構造方法執行

        Student s2 = new Student("derek", 18);   //全參構造方法執行
    }
}

1.4.Scanner類

package derek.learn;

//1.導包
import java.util.Scanner;

public class DemoScanner {
    public static void main(String[] args) {
        //2.創建，System.in代表從鍵盤進行輸入
        Scanner sc = new Scanner(System.in);
        //3.使用,獲取鍵盤輸入的int數字
        int num = sc.nextInt();
        System.out.println(num);
        //字元串
        String name = sc.next();
        System.out.println(name);
    }
}

1.5.Random類

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) {
        //創建一個ArrayList集合，裡面是String類型的數據
        ArrayList<String> list = new ArrayList<>();
        System.out.println(list);   //[]

        //1.向集合中添加數據
        list.add("迪麗熱巴");
        list.add("古力娜扎");
        list.add("馬爾扎哈");
        System.out.println(list);    //[迪麗熱巴, 古力娜扎, 馬爾扎哈]

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

        //3.刪除
        list.remove(1);
        System.out.println(list);    //[迪麗熱巴, 馬爾扎哈]

        //4.獲取集合長度
        System.out.println(list.size());    //2

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

1.7.String類

package derek.learn;

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

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

        //3.獲取子字元串的索引
        System.out.println(str3.indexOf('e'));    //6

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

        //5.轉換成為字元數組
        char[] chars = "Hello".toCharArray();
        System.out.println(chars[1]);   //e

        //6.替換
        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
    }
}