学习java第三天，跟着老师每天不断学习进步一点，大家一起加油鸭

今天学习了算术运算符、关系运算符、自增自减运算符、逻辑运算符，每天进步一点。
其中自增自减运算符在变量前，首先执行自增自减操作，再来完成当期行代码；变量在后，首先执行代码，再来执行自增自减操作。

class Demo1{
public static void main(String[] agrs){
//运算符 + - * /
int num = 10;
int num1 = 20;

num = num + num1;
num = num - num1;
num = num * num1;
num = num / num1;

System.out.println(num);
System.out.println(num1);

//偷懒运算符 += -= *= /=
int num2 = 12;
int num3 = 4;

num2 += num3;
num2 -= num3;
num2 *= num3;
num2 /= num3;

System.out.println(num2);
System.out.println(num3);

//关系运算符 < > <= >= != ==
boolean ret = true;

ret = 4 > 2 ;

System.out.println(ret);

ret = 3 < 6;

System.out.println(ret);

ret = 4 <= 5;

System.out.println(ret);

ret = 3 >= 4;

System.out.println(ret);

ret = 5 != 8;

System.out.println(ret);

ret = 4 == 6;

System.out.println(ret);

//自增自减运算符
int num4 = 3;

System.out.println(“num4 : " + num4);
System.out.println(”++num4 : " + num4++);
System.out.println("–num4 : " + num4++);
System.out.println("–num4 ：" + --num4);

//逻辑运算符
boolean ret1 = false;

ret1 = 4 > 3 && 5 >1;

System.out.println(ret1);

ret1 = 4 > 1 && 3 > 5;

System.out.println(ret1);

ret1 = 3 > 1 || 4 < 5;

System.out.println(ret1);

ret1 = 4 > 2 || 5 > 2;

System.out.println(ret1);

ret1 = !(5 < 6);

System.out.println(ret1);

ret1 = !(3 > 1);

System.out.println(ret1);

//逻辑运算符与短路原则问题
boolean ret2= false;
int num5 = 24;

ret2 = ++num5 > 28 && --num5 < 30;

System.out.println("ret2 : " +ret2);
System.out.println("num5 : " +num5);

ret2 = num5 < 27 || ++num5 > 20;

System.out.println("ret2 : " +ret2);
System.out.println("num5 : " +num5);

//小练习
//数字字符
boolean ret4 = false;
char ch = ‘0’;
ret4 = ch <= ‘9’ && ch >= ‘0’;

System.out.println(ret4);

//数值0 ~ 9
boolean ret3 = true;
int num6 = 0;
ret3 = num6 >= 0 && num6 <= 9;

System.out.println(ret3);

}

}