Java 基本語法---Java運算符

0. 概述

Java中的運算符主要分為以下幾種：

• 算術運算符
• 賦值運算符
• 關系運算符
• 邏輯運算符
• 條件運算符
• 位運算符
• 其他運算符

1. 算術運算符

public class ArithmeticTest {
    public static void main(String[] args) {
        double number1 = 12.390;
        double number2 = 74.340;
        int number3 = 4;

        System.out.println(number2 + " + " + number1 + " = " + (number2 + number1));
        System.out.println(number2 + " - " + number1 + " = " + (number2 - number1));
        System.out.println(number1 + " * " + number3 + " = " + (number1 * number3));
        System.out.println(number2 + " / " + number1 + " = " + (number2 / number1));
        System.out.println(number1 + " % " + number3 + " = " + (float)(number1 % number3));

        int number4 = 5;
        int number5 = 5;
        int number = number4++;
        System.out.println("number4++ = " + number + ", number4 = " + number4);

        number = ++number5;
        System.out.println("++number5 = " + number + ", number5 = " + number5);

        System.out.println("(number++) = " + (number++));;
        System.out.println("(number--) = " + (number--));
    }
}

Output：
    74.34 + 12.39 = 86.73
    74.34 - 12.39 = 61.95
    12.39 * 4 = 49.56
    74.34 / 12.39 = 6.0
    12.39 % 4 = 0.39
    number4++ = 5, number4 = 6
    ++number5 = 6, number5 = 6
    (number++) = 6
    (number--) = 7
 

2. 賦值運算符

public class AssignmentTest {
    public static void main(String[] args) {
        int a = 100;
        int b = 200;
        int c = 4;

        System.out.println("a (a += b) = " + (a += b));
        System.out.println("a (a -= 100) = " + (a -= 100));
        System.out.println("a (a *= c) = " + (a *= c));
        System.out.println("a (a /= 100) = " + (a /= 100));
        System.out.println("a (a %= 100) = " + (a %= 100));
        System.out.println("c ( c<<2 ) = " + ( c << 2 ));
        System.out.println("c ( c>>2 ) = " + ( c >> 2 ));
        
    }
}

Output：
    a (a += b) = 300
    a (a -= 100) = 200
    a (a *= c) = 800
    a (a /= 100) = 8
    a (a %= 100) = 8
    c ( c<<2 ) = 16
    c ( c>>2 ) = 1
 

3.關系運算符

public class RelationalTest {
    public static void main(String[] args) {
        int a = 100;
        int b = 88;

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

Output：
    (a == b) = false
    (a != b) = true

    (a <= b) = false
    (a >= b) = true

    (a > b) = true
    (a < b) = false

4. 邏輯運算符

public class LogicalTest {
    public static void main(String[] args) {
        boolean a = true;
        boolean b = false;

        System.out.println("(a && b) = " + (a && b));
        System.out.println("(a || b) = " + (a || b));
        System.out.println("!(a && b) = " + !(a && b));

        //短路邏輯運算符&&：先判斷前一個條件，true則執行第二個判斷操作，為false則不在執行
        int c = 100;
        System.out.println((c > 100) && (c++ < 150));
        System.out.println("c = "  + c);
        System.out.println();
        System.out.println((c++ < 150) && (c > 100));
        System.out.println("c = "  + c);
    }
}

Output：
    (a && b) = false
    (a || b) = true
    !(a && b) = true
    false
    c = 100

    true
    c = 101

5. 條件運算符

運算符有3個操作數，需要判斷布爾表達式的值。該運算符的主要是決定哪個值應該賦值給變量。

eg: a = ( b == 1) ? 20 : 30 ;

這一條語句：先判斷 b是否為1，為 true 則將 a設置為 20，為 false 則將 b 設置為 30；

public class ConditionalTest {
    public static void main(String[] args) {
        int a;
        int b = 100;

        a = (b == 100) ? 66 : 88;
        System.out.println("a =" + a);
        System.out.println();
        b = (a == 66) ? 888 : 88;
        System.out.println("b =" + b);
    }
}

Output：
a =66

b =888

6.案例

判斷輸入的年份是否為閏年；

LeapYear : 能被400整除的年份和能被4整除但是不能被100整除的年份

public class LeapYearDemo {
    //LeapYear:能被400整除的年份和能被4整除但是不能被100整除的年份
    public static void main(String[] args) {
        System.out.println("請輸入要判斷的年份： ");
        Scanner sc = new Scanner(System.in);
        int year = sc.nextInt();

        if ((year % 400 == 0) || (year % 4 == 0 && year %100 != 0 ))
        {
            System.out.println(year + "是閏年！");
        }
        else
        {
            System.out.println(year + "不是閏年！");
        }
    }
}


Output：
    請輸入要判斷的年份： 
    1997
    1997不是閏年！
    
    請輸入要判斷的年份： 
    2020
    2020是閏年！

Java 基本語法---Java運算符