运算符和包机制

1.运算符

package operator;

public class Demo01 {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        int c = 25;
        int d = 25;
        System.out.println(a+b);
        System.out.println(a-c);
        System.out.println(a*d);
        System.out.println(a/(double)b);
    }
}

package operator;

public class Demo02 {
    public static void main(String[] args) {
        long a = 53215631351631L;
        int  b = 20;
        short c = 10 ;
        byte d =15;
        System.out.println(a+b+c+d);//long
        System.out.println(b+c+d);//int
        System.out.println(c+d);//int

    }
}

package operator;

public class Demo03 {
    public static void main(String[] args) {
        //关系运算符返回的结果,正确,错误  布尔值
        int a = 10;
        int b = 20;
        int c = 21;

        System.out.println(c%b);//1
        System.out.println(a > b);
        System.out.println(a < b);
        System.out.println(a == b);
        System.out.println(a != b);
    }
}

package operator;

public class Demo04 {
    public static void main(String[] args) {
        //++  -- 自增自减运算符 一元运算符
        int a = 3;
        int b = a++;//执行完这行代码后,先给b赋值,再自增
        int c = ++a;//执行完这行代码后,先自增,再给b赋值
        System.out.println(a);//5
        System.out.println(b);//3
        System.out.println(c);//5

        //2^3 很多时候我们会用到数学工具类
        double pow = Math.pow(2, 3);//8.0
        System.out.println(pow);
    }


}

package operator;

public class Demo05 {
    public static void main(String[] args) {
        //and(与) or(或) 非（取反）
        boolean a = true;
        boolean b = false;
        System.out.println("a && b:" + (a&&b));//false 逻辑与运算，两个变量结果都为真，结果才为true
        System.out.println("a || b:" + (a||b));//true 逻辑或运算，两个变量有一个为真，结果才为true
        System.out.println("!(a && b):" + !(a && b));//true 如果为真，则变为假，如果为假则变为真

    //短路运算
        int c = 5;
        boolean d = (c < 4)&& (c++ < 4);
        System.out.println(c);//5
        System.out.println(d);//false

    }
}

package operator;

public class Demo06 {
    public static void main(String[] args) {
        // 左移 << *2   右移 >> /2
        System.out.println(2<<3);//2左移三位   16
    }
}

package operator;

public class Demo07 {
    public static void main(String[] args) {
        int a = 10;
        int b = 20;
        a += b;//a = a+b
        a -= b;//a = a-b

        System.out.println(a);
        //字符串连接符 +   String
        System.out.println(""+a+b);//1020
        System.out.println(a+b+"");//30
    }
}

package operator;

public class Demo08 {
    public static void main(String[] args) {
        //x ? y : z
        //如果x == true ,则结果为y，否则结果为z
        int score = 80;
        String type =score > 60 ? "及格" : "不及格";//必须掌握

        System.out.println(type);
    }
}

2.包机制

3.JavaDoc