基本运算符,自增自减运算符，初识Math类

 

 

instance of　　也是运算符，面向对象 时再说

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

package operator;

public class Demo01 {
    public static void main(String[] args) {
        //二元运算符
        //Ctrl + D : 复制当前行到下一行
        int a = 10;
        int b = 20;
        int c = 30;
        int d = 40;

        System.out.println(a+b);
        System.out.println(a-b);
        System.out.println(a*b);
        System.out.println(a/b);
        System.out.println(a/(double)b);
    }
}

"D:\IDEA java\IntelliJ IDEA 2019.3.5\jbr\bin\java.exe" "-javaagent:D:\IDEA java\IntelliJ IDEA 2019.3.5\lib\idea_rt.jar=57045:D:\IDEA java\IntelliJ IDEA 2019.3.5\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\L12\Desktop\Note\Demo1\out\production\Demo1 operator.Demo01
30
-10
200
0
0.5

Process finished with exit code 0

 

 

 不能把 int 类型转换为String,说明(c+d)也是int类型

 

 

package operator;

public class Demo02 {
    public static void main(String[] args) {
        long a = 123123123123123L;
        int b = 123;
        short c = 10;
        byte d = 8;

        //如果多个操作数中，有一个数为long,那么这个结果类型也为long
        // 如果多个操作数中，有一个数为double,那么这个结果类型也为double
        //如果没有long的时候，结果都为int
        System.out.println(a+b+c+d);//Long
        System.out.println(b+c+d);//Int
        System.out.println(c+d);//Int
        System.out.println((double)c+d);
        //System.out.println((string)(c+d));
    }
}

"D:\IDEA java\IntelliJ IDEA 2019.3.5\jbr\bin\java.exe" "-javaagent:D:\IDEA java\IntelliJ IDEA 2019.3.5\lib\idea_rt.jar=56218:D:\IDEA java\IntelliJ IDEA 2019.3.5\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\L12\Desktop\Note\Demo1\out\production\Demo1 operator.Demo02
123123123123264
141
18
18.0

Process finished with exit code 0

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
        //会大量的和     if  使用

        int a = 10;
        int b = 20;
        int c = 21;

        //取余，模运算
        System.out.println(c%a);//c/a   21/10=2...1

        System.out.println(a>b);
        System.out.println(a<b);
        System.out.println(a==b);
        System.out.println(a!=b);
    }
}

"D:\IDEA java\IntelliJ IDEA 2019.3.5\jbr\bin\java.exe" "-javaagent:D:\IDEA java\IntelliJ IDEA 2019.3.5\lib\idea_rt.jar=60751:D:\IDEA java\IntelliJ IDEA 2019.3.5\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\L12\Desktop\Note\Demo1\out\production\Demo1 operator.Demo03
1
false
true
false
true

Process finished with exit code 0

 自增，自减运算符　　重点会用在循环

快捷键

 

 

 

　　

 

package operator;

public class Demo04 {
    public static void main(String[] args) {
        //++    --  自增，自减   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
        //a=a+1
        System.out.println(a);//说明a++执行完的下一句，a才会加1
        //a=a+1
        int c = ++a;//++a   a=a+1//执行完这行代码前，先自增，再给c赋值

        System.out.println(a);
        System.out.println(b);
        System.out.println(c);

       /* for (int i = 0; i < ; i++) {

        }
        a++ + ++b
        */

       //运算符扩展 初识Math类
       //幂运算2^3 2*2*2 = 8   借助一些工具类  很多运算，我们会使用一些工具类来操作！
        double pow = Math.pow(2, 3);
        System.out.println(pow);
    }
}

"D:\IDEA java\IntelliJ IDEA 2019.3.5\jbr\bin\java.exe" "-javaagent:D:\IDEA java\IntelliJ IDEA 2019.3.5\lib\idea_rt.jar=61179:D:\IDEA java\IntelliJ IDEA 2019.3.5\bin" -Dfile.encoding=UTF-8 -classpath C:\Users\L12\Desktop\Note\Demo1\out\production\Demo1 operator.Demo04
4
5
3
5
8.0

Process finished with exit code 0