java数据类型

public class Demo01 {
    public static void main(String[] args) {
        //字符串
        String a = "中国";
        //整数
        int a1 = 10;
        byte aa = 127; //最大值到127
        long a2 = 30L; //long类型要在数字后面加个L
        //小数：浮点数
        float a3 = 10.2F;  //float类型要在数字后面加F
        double a4 = 3.14159;
        //字符
        char sex = '男';
        //布尔值
        boolean zhen = true;
    }
}

数据类型扩展

public class Demo2 {
    public static void main(String[] args) {
        //整数扩展： 进制  二进制0b  十进制  八进制0  十六进制0x
        int i = 10;
        int i2 = 010;//八进制0
        int i3 = 0x10;//十六进制0x
        System.out.println(i);//10
        System.out.println(i2);//8
        System.out.println(i3);//16

        //转义字符
        // \t制表符
        // \n换行
        System.out.println("Hool\tword");
        System.out.println("hoot\nword");

        //  == 判断是否相等
        String xa = "Hallo";
        String xb = "Hallo";
        System.out.println(xa == xb);

        //布尔值扩展
        boolean foot = false;
        if(foot == false){}//新手
        if(foot){}//老手
        //代码要精简易读
    }
}

类型转换

public class Demo3 {
    public static void main(String[] args) {
        int aa = 127;
        //强制转换，（类型）变量名   高--低
        byte bb = (byte)aa;
        //自动转换 低--高
        double cc = aa;
        System.out.println(aa);//127
        System.out.println(bb);//127
        System.out.println(cc);//127.0
        //char类型输出是d的下一位e
        System.out.println("=======================");
        char a = 'd';
        int b = a+1;
        System.out.println(b);//101
        System.out.println((char)b);//e
    }
}

较大数字类型转换用long

public class Demo4 {
    public static void main(String[] args) {
        //操作比较大的数字时要转换为long类型
        int money = 10_0000_0000;//数字较大时可以用下划线隔开
        int years = 20;

        int total1 = money * years;
        System.out.println(total1);//-1474836480，计算的时候溢出

        long total2 = money * years;
        System.out.println(total2);//-1474836480，要强制类型转换

        long total = money * ((long)years);
        System.out.println(total);//20000000000
    }
}