要求两个线程，同时打印字母，每个线程都能连续打印3个字母。两个线程交替打印，一个线程打印字母的小写形式，一个线程打印字母的大写形式，但是字母是连续的。当字母循环到z之后，回到a。

同步代码块实现：

public class Test2 {
    public static void main(String[] args) {
            Letter letter=new Letter();
            letter.letter='a';
            printLower p1= new printLower();
            printUpper p2 =new printUpper();
            p1.setLetter(letter);
            p2.setLetter(letter);
            p1.start();
            p2.start();
        }
    }
class printLower extends Thread {
   Letter letter;

        public void setLetter(JAVA.ThreadAPI.src.java.Letter letter) {
            this.letter = letter;
        }

        @Override
        public void run() {
            while (true) {
                synchronized (letter) {
                    for (int i=1;i<=3;i++){
                        System.out.println(Thread.currentThread().getName() + "->" + letter.letter);
                        letter.letter++;
                        if (letter.letter > 'z') {
                            letter.letter = 'a';
                        }
                        letter.notify();
                    }
                    try {
                        letter.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }


                }
            }
        }
    }
class printUpper extends Thread{
        Letter letter;

        public void setLetter(JAVA.ThreadAPI.src.java.Letter letter) {
            this.letter = letter;
        }

        @Override
        public void run() {
            while (true) {
                synchronized (letter){
                    for (int i=1;i<=3;i++){
               System.out.println(Thread.currentThread().getName() + "->" + (char)(letter.letter-32));
                        letter.letter++;
                        if (letter.letter > 'z') {
                            letter.letter = 'a';
                        }
                        letter.notify();
                    }
                    try {
                        letter.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }
            }
        }
    }
class Letter{
        char letter;
    }

同步方法实现：

public class Test2 {
    public static void main(String[] args) {
            Letter letter=new Letter();
            letter.letter='a';
            printLower p1= new printLower();
            printUpper p2 =new printUpper();
            p1.setLetter(letter);
            p2.setLetter(letter);
            p1.start();
            p2.start();
        }
    }
    class printLower extends Thread {
   Letter letter;

        public void setLetter(JAVA.ThreadAPI.src.java.Letter letter) {
            this.letter = letter;
        }

        @Override
        public void run() {
            while (true) {
                synchronized (letter) {
                    for (int i=1;i<=3;i++){
                        System.out.println(Thread.currentThread().getName() + "->" + letter.letter);
                        letter.letter++;
                        if (letter.letter > 'z') {
                            letter.letter = 'a';
                        }
                        letter.notify();
                    }
                    try {
                        letter.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }


                }
            }
        }
    }
    class printUpper extends Thread{
        Letter letter;

        public void setLetter(JAVA.ThreadAPI.src.java.Letter letter) {
            this.letter = letter;
        }

        @Override
        public void run() {
            while (true) {
                synchronized (letter){
                    for (int i=1;i<=3;i++){
                        System.out.println(Thread.currentThread().getName() + "->" + (char)(letter.letter-32));
                        letter.letter++;
                        if (letter.letter > 'z') {
                            letter.letter = 'a';
                        }
                        letter.notify();
                    }
                    try {
                        letter.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }
            }
        }
    }
    class Letter{
        char letter;
    }