System.out.println(0.1 + 0.2); // 输出 0.30000000000000004

BigDecimal a = new BigDecimal("0.1");
BigDecimal b = new BigDecimal("0.2");
System.out.println(a.add(b)); // 精确输出 0.3

// 1. 字符串构造（最安全）
BigDecimal d1 = new BigDecimal("0.1"); 

// 2. 使用 valueOf（内部调用 toString）
BigDecimal d2 = BigDecimal.valueOf(0.1); 

BigDecimal num1 = new BigDecimal("10");
BigDecimal num2 = new BigDecimal("3");

BigDecimal sum = num1.add(num2);      // 加法: 13
BigDecimal diff = num1.subtract(num2); // 减法: 7
BigDecimal product = num1.multiply(num2); // 乘法: 30

// 错误：无限小数会抛出 ArithmeticException
// BigDecimal result = num1.divide(num2); 

// 正确：指定保留3位小数，四舍五入
BigDecimal quotient = num1.divide(num2, 3, RoundingMode.HALF_UP); // 3.333

//设置小数位数
BigDecimal num = new BigDecimal("3.14159");

// 保留两位小数（四舍五入）
BigDecimal scaled = num.setScale(2, RoundingMode.HALF_UP); // 3.14

// 直接截断
BigDecimal truncated = num.setScale(2, RoundingMode.DOWN); // 3.14（若为 3.149→3.14）

BigDecimal x = new BigDecimal("1.0");
BigDecimal y = new BigDecimal("1.00");
x.compareTo(y);  // 返回 0（数值相等）

x.equals(y); // false（因为精度不同：1.0的scale=1, 1.00的scale=2）

  public class Test {
    public static void main(String[] args) {
        int a = 1;
        int b = 1;
        System.out.println(a++);//1
        System.out.println(++b);//2
    }
}

public class Test {
    public static void main(String[] args) {
        //1.求1-5之间的和
        int count = 0;
        for (int i = 1; i <= 5; i++) count += i;
        System.out.println(count);//15
    }
}

public class Test {
    public static void main(String[] args) {
        int count = 0;
        for (int i = 1; i <= 100; i++) {
            if (i % 2 == 0) count += i;
        }
        System.out.println(count);//2550
    }
}

public class Test {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入一个整数");
        int x = sc.nextInt();
        if (x < 2) throw new Error("请输入一个大于等于2的整数");
        int result = 0;
        while (result * result <= x) result++;
        System.out.println(result - 1);
    }
}

import java.util.Random;
import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        int num = r.nextInt(100) + 1;
        Scanner sc = new Scanner(System.in);
        System.out.println("值为" + num);
        while (true) {
            System.out.println("请输入一个整数");
            int inputNum = sc.nextInt();
            if (inputNum > num) System.out.println("猜大了");
            else if (inputNum < num) System.out.println("猜小了");
            else {
                System.out.println("猜对了");
                break;
            }
        }
    }
}

public class Test {
    public static void main(String[] args) {
        int[] arr = new int[]{1, 2, 3, 4, 5};
        //简写
        int[] arr2 = {1, 2, 3, 4, 5};
    }
}

public class Test {
    public static void main(String[] args) {
        int[] arr = new int[]{1, 2, 3, 4, 5};
        System.out.println(arr);//[I@1b6d3586
    }
}

public class Test {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        for (int i : arr) System.out.println(i);
    }
}

public class Test {
    public static void main(String[] args) {
        int[] arr1 = {1, 2, 3, 4, 5};
        int count = 0;
        for (int j : arr1) count += j;
        System.out.println(count);
    }
}

 public class Test {
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};
        int count = 0;
        for (int i : arr) i % 3 == 0 && count++;
        System.out.println(count);
    }
}

public class Test {
    public static void main(String[] args) {
        int[] arr = new int[10];
        int count = 0;
        Random r = new Random();
        for (int i : arr) {
            int num = r.nextInt(100) + 1;
            count += num;
            arr[i] = num;
        }
        //和
        System.out.println("和" + count);
        //平均值
        int average = count / arr.length;
        System.out.println("平均值" + average);
        //统计有多少个数据比平均值小
        int count1 = 0;
        for (int i : arr) if (i < average) count1++;
        System.out.println("总共有" + count1 + "个数比平均值小");
    }
}

public class Test {
    //1.成员变量（代表属性）
    //2.成员方法（代表行为）
}

public class Text {
    int number;

    private Phone(int number) {
        this.number = number;
    }
}

//people.java类
package text;

import java.util.Random;

public class People {
    //角色姓名
    private String name;
    //角色血量
    private int blod;
    //角色性别
    private char sex;
    //角色长相
    private String appearance;
    //男生长相数组
    String[] manFace = {"风流俊雅", "气宇轩昂", "英俊潇洒", "五官端正", "相貌平平", "喜气洋洋", "大长腿", "高冷", "短发", "长发"};
    //女生长相数组
    String[] womanFace = {"美奂绝伦", "沉鱼落雁", "婷婷玉立", "身材较好", "相貌平平", "相貌简陋", "长发", "短发"};
    //攻击描述
    String[] attackDescArr = {"%s使出一招【普心钉】，转到敌方身后，一掌向%s的灵台穴拍去。",
            "%s使出了一招【游空探爪】，飞起身形自半空中变掌为抓锁向%s。",
            "%s大喝一声，身形下伏，一招【劈雷坠地】，捶向%s双腿",
            "%s运气于掌，一瞬间掌心变得血红，一式【掌心雷】，推向%s。",
            "%s上步抢身，招中套招,一招【劈挂连环】,连环攻向%s",
            "%s阴手翻起阳手跟进，一招【没选拦】，结结实实的捶向%s"
    };
    //受伤描述
    String[] hurtDescArr = {"结果%s退了半步，毫发无损",
            "结果给%s造成一处瘀伤",
            "结果一击命中，%s痛得弯下腰",
            "结果%s痛苦地闷哼了一声，显然受了点内伤",
            "结果%s摇摇晃晃，一跤摔倒在地",
            "结果『轰』的一声，%s口中鲜血狂喷而出",
            "结果%s脸色一下变得惨白，连退了好几步",
            "结果%s一声惨叫，像滩软泥般塌了下去"
    };

    public People(String name, int blod, char sex) {
        this.name = name;
        this.blod = blod;
        setSex(sex);
    }

    public People() {
    }

    public char getSex() {
        return sex;
    }

    public void setSex(char sex) {
        this.sex = sex;
        Random random = new Random();
        if (sex == '男') {
            int r = random.nextInt(manFace.length);
            setAppearance(manFace[r]);
        } else if (sex == '女') {
            int r = random.nextInt(womanFace.length);
            setAppearance(womanFace[r]);
        }
    }

    public String getAppearance() {
        return appearance;
    }

    public void setAppearance(String appearance) {
        this.appearance = appearance;
    }

    /**
     * 获取
     *
     * @return name
     */
    public String getName() {
        return name;
    }

    /**
     * 设置
     *
     * @param name
     */
    public void setName(String name) {
        this.name = name;
    }

    /**
     * 获取
     *
     * @return blod
     */
    public int getBlod() {
        return blod;
    }

    /**
     * 设置
     *
     * @param blod
     */
    public void setBlod(int blod) {
        this.blod = blod;
    }

    //角色发起攻击
    public void attack(People people) {
        Random r = new Random();
        //获取随机攻击描述
        String attackDesc = attackDescArr[r.nextInt(attackDescArr.length)];
        System.out.printf(attackDesc, this.name, people.name);
        //获取随机伤害
        int hurt = r.nextInt(10) + 1;
        //计算剩余血量
        int remainBlode = people.getBlod() - hurt;
        people.setBlod(Math.max(remainBlode, 0));
        //获取受伤描述
        String hurtDesc = "";

        int blod = people.getBlod();
        if (blod > 90) hurtDesc = hurtDescArr[0];
        else if (blod > 80) hurtDesc = hurtDescArr[1];
        else if (blod > 70) hurtDesc = hurtDescArr[2];
        else if (blod > 60) hurtDesc = hurtDescArr[3];
        else if (blod > 50) hurtDesc = hurtDescArr[4];
        else if (blod > 40) hurtDesc = hurtDescArr[5];
        else if (blod > 0) hurtDesc = hurtDescArr[6];
        else hurtDesc = hurtDescArr[7];
        System.out.printf(hurtDesc, people.name);
        System.out.print(",造成" + hurt + "点伤害," + people.name + "剩余" + people.getBlod() + "血量");
        System.out.println();
    }

    //展示角色信息
    public void show() {
        System.out.println("姓名:" + getName() + "  血量:" + getBlod() + "  性别:" + getSex() + "  长相:" + getAppearance());
    }
}


//使用
//main.java
import text.People;

public class Main {
    public static void main(String[] args) {
        //文字攻击
        People people1 = new People("James", 100, '男');
        People people2 = new People("Tom", 100, '女');
        people1.show();
        people2.show();
        while (true) {
            people1.attack(people2);
            if (people2.getBlod() <= 0) {
                System.out.println(people1.getName() + "已经死亡,战斗结束");
                break;
            }
            people2.attack(people1);
            if (people1.getBlod() <= 0) {
                System.out.println(people2.getName() + "已经死亡,战斗结束");
                break;
            }
        }
    }
}

//声明类
public class phone {
    private int price;
    private String brand;
    private String color;

    public void setPrice(int p) {
        this.price = p;
    }

    public int getPrice() {
        return this.price;
    }

    public void call(String name) {
        System.out.println("正在给" + name + "打电话");
    }

    public void sendMessage(String name) {
        System.out.println("正在给" + name + "发短信");
    }
}


//使用类
public class Main {
    public static void main(String[] args) {
        phone myPhone = new phone();
        myPhone.call("James");//正在给James打电话
        myPhone.setPrice(2399);
        System.out.println("手机机价格是" + myPhone.getPrice());//手机机价格是2399
    }
}

package api;

import java.util.Arrays;
import java.util.Comparator;

public class LambdaText {
    public static void main(String[] args) {
        Integer[] arr = {1, 4, 2, 6, 4, 3, 8, 9, 7, 5};
        Arrays.sort(arr, new Comparator<Integer>() {
            @Override
            public int compare(Integer o1, Integer o2) {
                return o1 - o2;
            }
        });
        System.out.println(Arrays.toString(arr));


        //使用Lambda表达式简化匿名内部类
        Integer[] arr2 = {1, 4, 2, 6, 4, 3, 8, 9, 7, 5};
        Arrays.sort(arr2, (o1, o2) -> {
            return o1 - o2;
        });
        System.out.println(Arrays.toString(arr2));
    }

}

public class LambdaText {
    public static void main(String[] args) {
        scText(new Swim() {
            @Override
            public void swiming() {
                System.out.println("我在游泳");
            }
        });
        //使用lambda表达式简化
        scText(() -> System.out.println("我在游泳"));
    }

    //调用方法的时候如果这个方法的形参是一个接口，那么我们就要传递这个接口的实现类对象
    //如果实现类对象只要用到一次，就可以使用Lambda表达式来简化
    public static void scText(Swim swim) {
        swim.swiming();
    }

    //使用匿名内部类的前提该要是一个接口 不能是抽象类
    @FunctionalInterface //该注解表示这是一个函数式接口，只有一个抽象方法
    interface Swim {
        public abstract void swiming();
        //   public abstract void swimings();报错
    }
}

class GF {
    String name;
    int age;
    double height;

    public GF(String name, int age, double height) {
        this.name = name;
        this.age = age;
        this.height = height;
    }

    public class LambdaText {
        public static void main(String[] args) {
            //练习
            //定义第一个存储字符串的数组 字符短的在前面 长的在后面
            String[] arr3 = {"aaaa", "aa", "a", "aaa", "aaaa"};
            Arrays.sort(arr3, (o1, o2) -> o1.length() - o2.length());
            System.out.println(Arrays.toString(arr3));//[a, aa, aaa, aaaa, aaaa]

            //定义数组并存储一些女朋友对象，利用Arrays中的sort方法进行排序
            //要求：属性有姓名。年龄、身高
            //要求2:按照年龄的大小进行排序，年龄一样的按照身高进行排序，身高一样的按照姓名字母进行排序


            GF[] arr4 = {new GF("小红", 18, 1.68), new GF("小明", 19, 1.70), new GF("小花", 18, 1.68)};
            Arrays.sort(arr4, (o1, o2) ->

            {
                if (o1.age != o2.age) return o1.age - o2.age;
                if (o1.height != o2.height) return (int) (o1.height - o2.height);
                //将字符串按照字典的顺序（Ascii码的顺序）进行比较
                return o1.name.compareTo(o2.name);
            });
            System.out.println(Arrays.toString(arr4));
        }
    }