Java 程序使用两个线程打印奇偶数

17 Mar 2025 | 4 分钟阅读

线程是多线程编程的一部分。要编写一个使用 2 个线程打印奇偶数的代码，需要了解多线程。

现在，我们需要使用两个不同的线程按自然顺序打印到MAX 的奇偶数。因此，我们有两种方法可以解决这个问题，即使用wait 和 notify 以及使用余数的概念。

使用 wait 和 notify

为了使用wait 和 notify 打印奇偶数，我们使用以下步骤：

我们创建一个布尔变量odd，当我们需要打印奇数时，其值为 true。
我们创建两个用户定义的方法，例如printEventNumbers() 和printOddNumbers()，用于打印偶数和奇数。
我们同时创建两个线程，即 thread1 和 thread2，分别用于偶数和奇数。
thread1 将同时调用 printEvenNumbers() 方法，thread2 将同时调用 printOddNumbers() 方法。
在 printEvenNumbers() 方法中，thread1 将等待布尔值odd 为 true。
在 printOddNumbers() 方法中，thread2 将等待布尔值odd 为 false。

让我们使用wait 和 notify 来实现打印奇偶数代码。

PrintEvenOddExample1.java

// import required classes and package if any
import java.util.Scanner;
// create class PrintEvenOddExample1 to print even and odd numbers using two threads
public class PrintEvenOddExample1 {
    // create a boolean variable odd for even and odd numbers
    boolean odd;
    int counter = 1;	// set initial counter to 1
    int MAX;
    // create printOddNumbers() method to print odd numbers
    public void printOddNumbers() {
        // synchronized block for odd numbers
        synchronized (this) {
            while (counter < MAX) {
                System.out.println("Syncronized block call for odd numbers.");
                while (!odd) {	// use wait and notify technique within while loop
                    // call wait() method within try-catch block for
                    try {
                        // print odd that is waiting
                        System.out.println("Odd waiting : " + counter);
                        // call wait() method
                        wait();
                        //print odd that is notified
                        System.out.println("Notified odd :" + counter);
                    } catch (InterruptedException e) {
                        // handle exceptions 
                        e.printStackTrace();
                    }
                }
                // print odd thread
                System.out.println("Odd Thread :" + counter);
                // increment counter variable
                counter++;
                // set boolean odd to false
                odd = false;
                // call notify()
                notify();
            }
        }
    }
    // create printEvenNumbers() method to print even numbers
    public void printEvenNumbers() {
        // use try-catch block to sleep thread
        try {
            // stop thread for a specific time
            Thread.sleep(1000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
        // synchronized block for odd numbers
        synchronized (this) {
            while (counter < MAX) {
                System.out.println("Syncronized block call for even numbers.");
                while (odd) {	// use wait and notify technique within while loop
                    // call wait() method within try-catch block for
                    try {
                        // print odd that is waiting
                        System.out.println("Even waiting : " + counter);
                        // call wait() method
                        wait();
                        //print even that is notified
                        System.out.println("Notified even :" + counter);
                    } catch (InterruptedException e) {
                        // handle exceptions 
                        e.printStackTrace();
                    }
                }
                // print odd thread
                System.out.println("Even Thread :" + counter);
                // increment counter variable
                counter++;
                // set boolean odd to false
                odd = false;
                // call notify()
                notify();
            }
        }
    }
    // main() method start
    public static void main(String[] args) {
        // create an instance of PrintEvenOddExample1
        final PrintEvenOddExample1 obj = new PrintEvenOddExample1();
        // set boolean odd to true 
        obj.odd = true;
        // create an instance of Scanner class
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter MAX value:");
        obj.MAX = sc.nextInt();
        // close scanner class instance
        sc.close();
        // create thread1 to print even numbers
        Thread thread1 = new Thread(new Runnable() {
            // override run() method
            @Override
            public void run() {
                obj.printEvenNumbers();
            }
        });
        // create thread2 to print odd numbers
        Thread thread2 = new Thread(new Runnable() {
            // override run() method
            @Override
            public void run() {
                obj.printOddNumbers();
            }
        });
        // start thread1 and thread2
        thread1.start();
        thread2.start();
        // call join() method within try-catch block
        try {
            thread1.join();
            thread2.join();
        } catch (InterruptedException e) {
            // handle exception
            e.printStackTrace();
        }
    }
}

输出

Java Program to Print Even Odd Using Two Threads in

使用余数

在这种使用两个线程打印奇偶数的技术中，代码基于以下两点：

如果 num%2==1，则奇数线程打印该数字并将其递增。否则，奇数线程将进入等待状态。
如果 number%2==0，则偶数线程打印该数字并将其递增。否则，偶数线程将进入等待状态。

EvenOddRunnable.java

// import required classes and package if any
// create class EvenOddRunnable that implements runnable interface 
public class EvenOddRunnable implements Runnable{
    int MAX;
    static int  counter = 1;
    int rem;
    static Object lock = new Object();
    // parameterized constructor
    EvenOddRunnable(int rem, int MAX)
    {
        this.rem = rem;
        this.MAX = MAX;
    }
    // override run() method
    @Override
    public void run() {
    	// use while loop to recursively execute steps until counter < MAX
        while (counter < MAX) {
        	// synchronized block
            synchronized (lock) {
                while (counter % 2 != rem) { // wait for numbers other than remainder
                	// use try-catch block to put lock in waiting state
                    try {
                        lock.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.println(Thread.currentThread().getName() + " " + counter);
                //increment counter
                counter++;
                lock.notifyAll();
            }
        }
    }
}

PrintEvenOddExample2.java

// import required class and package if any
import java.util.Scanner;
// create class PrintEvenOddExample2 to print even and odd numbers using 2 threads
public class PrintEvenOddExample2 {
	public static void main(String[] args) {
		int MAX;
		// create an instance of Scanner class
		Scanner sc = new Scanner(System.in);
    	System.out.println("Enter MAX value:");
    	MAX = sc.nextInt();
    	// close scanner class instance
    	sc.close();
    	// create instances of EvenOddRunnable classes
    	EvenOddRunnable runnable1 = new EvenOddRunnable(1, MAX );
    	EvenOddRunnable runnable2 = new EvenOddRunnable(0, MAX);
    	// create thread1 and thread2
        Thread thread1 = new Thread(runnable1,"Odd");
        Thread thread2 = new Thread(runnable2,"Even");       
// use start() method to start thread1 and thread2
        thread1.start();
        thread2.start();
    }
}

输出

下一主题Java Variant

Java 程序使用两个线程打印奇偶数

使用 wait 和 notify

使用余数

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Java 程序使用两个线程打印奇偶数

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