Java3個編程題整理

1.代碼實作單例模式中的懶漢模式

/**
 * 單例模式中的懶漢模式
 */
public class LazySingleton {

    /**
     * 用volatile 修飾類變數
     */
    private static volatile LazySingleton singleton;

    /**
     * 構造器私有
     */
    private LazySingleton(){}

    /**
     * 雙重檢查
     * @return
     */
    public static LazySingleton getInstance(){
        if(singleton == null){
            synchronized (LazySingleton.class){
                if(singleton == null){
                    singleton = new LazySingleton();
                }
            }
        }
        return singleton;
    }


    /**
     * 測驗
     */
    public static void main(String[] args) {
        LazySingleton singleton1 = LazySingleton.getInstance();
        LazySingleton singleton2 = LazySingleton.getInstance();
        System.out.println("singleton1:"+singleton1);
        System.out.println("singleton2:"+singleton2);
        System.out.println(singleton1 == singleton2);
    }

}

2.撰寫一個Java程式在螢屏上輸出1！+2！+3！+...+10!的和

public class Factorial {

    /**
     * 用遍歷的方式解題
     */
    public static void traverseMethod() {
        int i, j, mul, sum = 0;
        for (i = 1; i <= 10; i++) {
            mul = 1;
            for (j = 1; j <= i; j++) {
                mul = mul * j;
            }
            sum = sum + mul;
        }
        System.out.println("1！+2！+3！+...+10!=" + sum);
    }

    /**
     * 用遞回的方式解題
     */
    public static void factorialMethod() {
        System.out.println("1！+2！+3！+...+10!="
                + (factorial(1) + factorial(2)
                + factorial(3) + factorial(4)
                + factorial(5) + factorial(6)
                + factorial(7) + factorial(8)
                + factorial(9) + factorial(10))

        );
    }

    public static int factorial(int num) {
        if (num == 1) {
            return 1;
        }
        return num * factorial(num - 1);
    }


    /**
     * 測驗
     */
    public static void main(String[] args) {
        traverseMethod();//4037913
        factorialMethod();//4037913
    }

}

3.設計一個生產電腦和搬運電腦類，要求生產一臺電腦就搬走一臺電腦，如果沒有新的電腦生產出來，則搬運工要等待新電腦產出；如果生產出的電腦沒有搬走，則要等待電腦搬走之后在生產，并統計出生產的電腦數量，

public class ComputerTest {

    public static void main(String[] args) throws InterruptedException {
        Computer computer = new Computer();

        Thread produceThread = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    computer.produceComputer();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "produceThread");
        produceThread.start();
        Thread carryThread = new Thread(() -> {
            for (int i = 0; i < 10; i++) {
                try {
                    computer.carryComputer();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, "carryThread");
        carryThread.start();

        produceThread.join();
        carryThread.join();
        
        System.out.printf("共生產了%s臺電腦\n", computer.getComputerCount());
    }

    /**
     * 電腦類
     */
    public static class Computer {
        /**
         * 生產出的電腦的數量
         */
        private int computerCount;
        //電腦是否不為空 true-不為空 false為空
        private volatile boolean flag;

        /**
         * 獲取生產出的電腦的數量
         *
         * @return
         */
        public int getComputerCount() {
            return computerCount;
        }

        /**
         * 生產電腦
         */
        public synchronized void produceComputer() throws InterruptedException {
            while (flag) {
                wait();
            }
            this.computerCount++;
            flag = true;
            System.out.printf("%s 開始生產電腦\n", Thread.currentThread().getName());
            notifyAll();
        }

        /**
         * 搬運電腦
         */
        public synchronized void carryComputer() throws InterruptedException {
            //讓搬運電腦消耗1秒鐘，看程式執行效果
            TimeUnit.SECONDS.sleep(1);
            while (!flag) {
                wait();
            }
            flag = false;
            System.out.printf("%s 開始搬運電腦\n", Thread.currentThread().getName());
            notifyAll();
        }

    }

}

標籤：Java

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