Java之路 - String类、static、继承、覆盖重写、super

public class DemoString {
    public static void main(String[] args) {
        //根据字符数组创建字符串
        char[] chararray = {'A','B','C'};
        String str1 = new String(chararray);
        System.out.println(str1);

        //根据字节数组创建字符串
        byte[] bytearray = { 97 , 98 , 99};
        String str2 = new String(bytearray);
        System.out.println(str2);

        //直接创建
        String str3 = "hello, i am chris";
        System.out.println(str3);
    }
}

第一种创建空字符串的省略了

public class StringMethod {
    public static void main(String[] args) {
        int[] array1 = {1, 2, 3};
        String result = arrraymethod(array1);
        System.out.println(result);
    }

    public static String arrraymethod(int[] array) {
        String result = "[";
        for (int i = 0; i < array.length; i++) {
            if (i == array.length - 1) {
                result += "word" + array[i] + "]";
            } else {
                result += "word" + array[i] + "#";
            }
        }
        return result;
    }
}

public class StringPractise {
    public static void main(String[] args) {
        Scanner s1 = new Scanner(System.in);
        System.out.println("请输入一个字符串：");
        String str = s1.next(); //获取键盘输入的字符串

        //创建四个计数器
        int countUpper = 0;
        int countLower = 0;
        int countNum = 0;
        int countOther = 0;

        //将字符串转换为字符数组
        char[] StringArray = str.toCharArray();
        for (int i = 0; i < StringArray.length; i++) {
            char charnow = StringArray[i]; //charnow表示的是遍历的当前字符
            if ('A' <= charnow && charnow <= 'Z'){  //因为字符类型在做数学运算时为自动提升为int类型 所以可以进行比较
                countUpper++;
            }else if('a' <= charnow && charnow <= 'z'){
                countLower++;
            }else if('0' <= charnow && charnow <= '9'){
                countNum++;
            }else {
                countOther++;
            }
        }
        System.out.println("大写字母有：" + countUpper +"个");
        System.out.println("小写字母有：" + countLower + "个");
        System.out.println("数字有：" + countNum + "个");
        System.out.println("其他字符有：" + countOther + "个");
    }
}

package basicpart.day01;

public class Student{
    private String name;
    private int age;
    private int id = 0;
    static String classroom = "七六班";
    private static int idCounter = 0;//学号计数器 每当有一个对象产生，计数器++ 外部不可访问

    public Student() {
    }

    public Student(String name, int age) {
        this.name = name;
        this.age = age;
        this.id = ++idCounter;
    }

    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 int getId() {
        return id;
    }

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

public class FaceObject {
    public static void main(String[] args) {
        String str1 = "asgewf2124sa14dsg";
        char[] charArray = str1.toCharArray(); // 先将字符串变为字符数组
        Arrays.sort(charArray); // 对字符数组进行升序排列

        for (int i = charArray.length-1; i >= 0; i--) { //倒序遍历 forr就是倒序
            System.out.println(charArray[i]);
        }
    }

}

public class FaceObject {
    public static void main(String[] args) {
        double min = - 10.8;
        double max = 5.9;
        int absCount = 0;
        //这样处理，就是区间之内所有的整数
        for(int i = (int) min; i < max; i++){
            int abs = Math.abs(i); //取绝对值
            
            if (abs > 6 || abs < 2.1){
                System.out.println(i);
                absCount++;
            }

        }
        System.out.println("总共有" + absCount +"个");
    }
}

父类：
public class Fu {
    int num = 10;
}

子类：
public class Zi extends Fu{
    int num = 20;
    public void ziMethod(){
        int num = 30;
        System.out.println(num); //输出的是局部变量num = 30
        System.out.println(this.num); //输出的是成员变量 num = 20
        System.out.println(super.num); //输出的是父类的成员变量 num = 10
    }
}

调用：
public class MainMethod {
    public static void main(String[] args) {
        Zi zi = new Zi();
        zi.ziMethod();
    }
}