变量与运算 ​

//例如：
//存储一个整数类型的年龄
int age; 

//存储一个小数类型的体重
double weight;

//存储一个单字符类型的性别 
char gender;

//存储一个布尔类型的婚姻状态
boolean marry;

//存储一个字符串类型的姓名
String name;

//声明多个同类型的变量
int a,b,c; //表示a,b,c三个变量都是int类型。

变量名 = 值;

age = 18;
weight = 109;
gender = '女';

int m = 1;
int n = m;
        
int x = 1;
int y = 2;
int z = 2 * x + y;

//先声明，后初始化
char gender;
gender = '女';

//给变量重新赋值，修改gender变量的值
gender = '男';
System.out.println("gender = " + gender);//gender = 男

boolean isBeauty = true;
String name = "迪丽热巴";

//测试1：（解释见章末企业真题：为什么0.1 + 0.2不等于0.3）
System.out.println(0.1 + 0.2);//0.30000000000000004

//测试2：
float ff1 = 123123123f;
float ff2 = ff1 + 1;
System.out.println(ff1);
System.out.println(ff2);
System.out.println(ff1 == ff2);

/**
 * @author 诗仙
 * @create 00:06
 */
public class Exercise1 {
    public static void main(String[] args) {
        double PI = 3.14; //圆周率

        double radius1 = 1.2;
        double radius2 = 2.5;
        int radius3 = 6;

        System.out.println("第1个圆的面积：" + PI * radius1 * radius1);
        System.out.println("第2个圆的面积：" + PI * radius2 * radius2);
        System.out.println("第3个圆的面积：" + PI * radius3 * radius3);
    }
}

/**
 * @author 诗仙
 * @create 00:08
 */
public class Exercise2 {
    public static void main(String[] args) {
        double hua = 80;
        double she = (hua-32)/1.8;
        System.out.println("华氏度" + hua+"℉转为摄氏度是" +she+"℃");
    }
}

boolean isFlag = true;

if(isFlag){
    //true分支
}else{  
    //false分支
}

/**
 * @author 张向阳
 * @create 10:23
 */
public class Info {
    public static void main(String[] args) {
        String name = "康师傅";
        int age = 37;
        char gender = '男';
        double weight = 145.6;
        boolean isMarried = true;
        String phoneNumber = "13112341234";

        System.out.println("姓名：" + name);
        System.out.println("年龄：" + age);
        System.out.println("性别：" + gender);
        System.out.println("体重：" + weight);
        System.out.println("婚否：" + isMarried);
        System.out.println("电话：" + phoneNumber);
		//或者
        System.out.println("name = " + name + ",age = " + age + "，gender = " + 
                           gender + ",weight = " + weight + ",isMarried = " + isMarried +
                           ",phoneNumber = " + phoneNumber);
    }
}

class CountExercise {
	public static void main(String[] args) {
		/**
			+	-	*	/	%	++	--
		*/
		
		// 除法（取整数）
		int n1 = 10;
		int n2 = 3;
		int result1 = n1 / n2;
		System.out.println("结果：" + result1);	  // 3
        
		// 取模（或取余）
		int n3 = 13;
		int n4 = 6;
		int result2 = n3 % n4;
		System.out.println("结果：" + result2);

		// 前++     （先运算(加加)，后赋值）
		int l1 = 5;
		int l2 = 2;
		++l2;
		System.out.println(l2);

		// 后++		（先赋值，后运算(加加)）
		int l3 = 5;
		int l4 = 1;
		l3++;
		System.out.println(l3);
        
		// 前--
		// 后--
	}
}

public class SetValueTest1 {
	public static void main(String[] args) {
		int i1 = 10;
		long l1 = i1; //自动类型转换

		byte bb1 = (byte)i1; //强制类型转换

		int i2 = i1;

		//连续赋值的测试
		//以前的写法
		int a1 = 10;
		int b1 = 10;
		
		//连续赋值的写法
		int a2,b2;
		a2 = b2 = 10;
		
		int a3 = 10,b3 = 20;

		//举例说明+=  -=  *=  /=   %=  
		int m1 = 10;
		m1 += 5; //类似于 m1 = m1 + 5的操作，但不等同于。
		System.out.println(m1);//15
		
		//练习1：开发中，如何实现一个变量+2的操作呢？
		// += 的操作不会改变变量本身的数据类型。其他拓展的运算符也如此。
		//写法1：推荐
		short s1 = 10;
		s1 += 2; //编译通过，因为在得到int类型的结果后，JVM自动完成一步强制类型转换，将int类型强转成short
		System.out.println(s1);//12
		//写法2：
		short s2 = 10;
		//s2 = s2 + 2;//编译报错，因为将int类型的结果赋值给short类型的变量s时，可能损失精度
		s2 = (short)(s2 + 2);
		System.out.println(s2);


		//练习2：开发中，如何实现一个变量+1的操作呢？
		//写法1：推荐
		int num1 = 10;
		num1++;
		System.out.println(num1);

		//写法2：
		int num2 = 10;
		num2 += 1;
		System.out.println(num2);

		//写法3：
		int num3 = 10;
		num3 = num3 + 1;
		System.out.println(num3);

	}
}

class CompareTest {
	public static void main(String[] args) {
		int i1 = 10;
		int i2 = 20;
		
		System.out.println(i1 == i2);//false
		System.out.println(i1 != i2);//true
		System.out.println(i1 >= i2);//false


		int m = 10;
		int n = 20;
		System.out.println(m == n);//false
		System.out.println(m = n);//20

		boolean b1 = false;
		boolean b2 = true;
		System.out.println(b1 == b2);//false
		System.out.println(b1 = b2);//true
	}
}

boolean b1 = false;
//区分好==和=的区别。
if(b1 == true)  //if(b1 = true)
	System.out.println("结果为真");
else
	System.out.println("结果为假");

public class LoginTest {
	public static void main(String[] args) {
		int a = 3;
		int b = 4;
		int c = 5;

		// & 与，且；有false则false
		System.out.println((a > b) & (a > c)); 
		System.out.println((a > b) & (a < c)); 
		System.out.println((a < b) & (a > c)); 
		System.out.println((a < b) & (a < c)); 
		System.out.println("===============");
		// | 或；有true则true
		System.out.println((a > b) | (a > c)); 
		System.out.println((a > b) | (a < c)); 
		System.out.println((a < b) | (a > c));
		System.out.println((a < b) | (a < c));
		System.out.println("===============");
		// ^ 异或；相同为false，不同为true
		System.out.println((a > b) ^ (a > c));
		System.out.println((a > b) ^ (a < c)); 
		System.out.println((a < b) ^ (a > c)); 
		System.out.println((a < b) ^ (a < c)); 
		System.out.println("===============");
		// ! 非；非false则true，非true则false
		System.out.println(!false);
		System.out.println(!true);
        
        //&和&&的区别
        System.out.println((a > b) & (a++ > c)); 
        System.out.println("a = " + a);
        System.out.println((a > b) && (a++ > c)); 
        System.out.println("a = " + a);
        System.out.println((a == b) && (a++ > c)); 
        System.out.println("a = " + a);
        
        //|和||的区别
        System.out.println((a > b) | (a++ > c)); 
        System.out.println("a = " + a);
        System.out.println((a > b) || (a++ > c)); 
        System.out.println("a = " + a);
        System.out.println((a == b) || (a++ > c)); 
        System.out.println("a = " + a);
	}
}

/**
 * @author 尚硅谷-宋红康
 * @create 12:42
 */
public class CompareLogicExer {
    public static void main(String[] args){
        int a = 20;
        int b = 20;
        boolean bo1 = ((++a % 3) == 0) && ((a++ % 7) == 0);
        System.out.println("bo1的值：" + bo1);
        System.out.println("a的值：" + a);
        System.out.println("----------------------------");
        
        boolean bo2 = ((b++ % 3) == 0) && ((++b % 7) == 0); 
        System.out.println("bo2的值：" + bo2);
        System.out.println("b的值：" + b);
    }
}

int x = 1;
int y = 1;

if(x++ == 2 & ++y == 2){
	x = 7;
}
System.out.println("x=" + x + ",y=" + y);

int x = 1,y = 1;

if(x++ == 2 && ++y == 2){
	x =7;
}
System.out.println("x="+x+",y="+y);

int x = 1,y = 1;

if(x++==1 | ++y==1){
	x =7;
}
System.out.println("x="+x+",y="+y);

int x = 1,y = 1;

if(x++==1 || ++y==1){
	x =7;
}
System.out.println("x="+x+",y="+y);

class  Test  {
	public static void main (String []  args)  {
		boolean x = true;
        boolean y = false;
        short z = 42;
        
        if ((z++ == 42) && (y = true)) {
            z++;
        }
        if ((x = false) || (++z == 45)) {
            z++;
        }

        System.out.println("z=" + z);
	}
}

//结果为：
//z= 46