智能医学工程-计算机程序设计-2025版-教学案例-第03章

eg 3.1

public class PrimitiveTypesDemo {
    public static void main(String[] args) {
        byte age = 18;
        short year = 2024;
        int population = 7800000000;
        long distance = 150000000000L;
        float pi = 3.14f;
        double e = 2.71828;
        char grade = 'A';
        boolean isJavaFun = true;

        System.out.println("Age: " + age);
        System.out.println("Year: " + year);
        System.out.println("Population: " + population);
        System.out.println("Distance: " + distance);
        System.out.println("Pi: " + pi);
        System.out.println("Euler's Number: " + e);
        System.out.println("Grade: " + grade);
        System.out.println("Is Java Fun: " + isJavaFun);
    }
}

eg 3.2

public class BuiltInTypesDemo {
    public static void main(String[] args) {
        String message = "Hello, Java!";
        int[] numbers = {1, 2, 3, 4, 5};

        System.out.println("Message: " + message);
        System.out.print("Numbers: ");
        for (int number : numbers) {
            System.out.print(number + " ");
        }
    }
}

eg 3.3.1

public class StringDemo {
    public static void main(String[] args) {
        String greeting = "Hello";
        String name = "World";
        String message = greeting + ", " + name + "!";
        
        System.out.println("Message: " + message);
        System.out.println("Uppercase: " + message.toUpperCase());
        System.out.println("Substring: " + message.substring(7));
    }
}

eg 3.3.2

public class StringBufferDemo {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer("Hello");
        sb.append(" World");
        sb.insert(5, ",");
        sb.replace(6, 11, "Java");

        System.out.println("StringBuffer: " + sb.toString());
    }
}

eg 3.4

public class WrapperClassDemo {
    public static void main(String[] args) {
        int num = 100;
        Integer numObj = Integer.valueOf(num); // 将 int 转换为 Integer 对象

        System.out.println("Primitive int: " + num);
        System.out.println("Wrapper Integer: " + numObj);

        // 自动装箱和拆箱
        Integer autoBoxed = num; // 自动装箱
        int autoUnboxed = autoBoxed; // 自动拆箱

        System.out.println("Auto-boxed Integer: " + autoBoxed);
        System.out.println("Auto-unboxed int: " + autoUnboxed);
    }
}

eg 3.5

import java.math.BigInteger;

public class BigIntegerDemo {
    public static void main(String[] args) {
        BigInteger bigNum1 = new BigInteger("123456789012345678901234567890");
        BigInteger bigNum2 = new BigInteger("987654321098765432109876543210");

        BigInteger sum = bigNum1.add(bigNum2);
        BigInteger product = bigNum1.multiply(bigNum2);

        System.out.println("Sum: " + sum);
        System.out.println("Product: " + product);
    }
}

eg 3.6.1

import java.util.Date;
import java.text.SimpleDateFormat;

public class DateDemo {
    public static void main(String[] args) {
        Date now = new Date();
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        System.out.println("Current Date: " + sdf.format(now));
    }
}

eg 3.6.2

import java.util.Calendar;

public class CalendarDemo {
    public static void main(String[] args) {
        Calendar cal = Calendar.getInstance();
        cal.add(Calendar.DAY_OF_MONTH, 5); // 加5天

        System.out.println("Date after 5 days: " + cal.getTime());
    }
}

eg 3.6.3

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class Java8DateTimeDemo {
    public static void main(String[] args) {
        LocalDateTime now = LocalDateTime.now();
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");

        System.out.println("Current DateTime: " + now.format(formatter));
    }
}