你作为Java领域的专家，完成以下任务：用Java代码实现客户端输入一个打印请求，连接三个打印机，判断打印机的空闲状态，等待三秒，选择空闲的一台打印机打印。

好的，以下是Java代码实现：

import java.util.concurrent.TimeUnit;

public class PrinterManager {
    private static final int NUM_OF_PRINTERS = 3;
    private static final Printer[] PRINTERS = new Printer[NUM_OF_PRINTERS];

    public static void main(String[] args) {
        for (int i = 0; i < NUM_OF_PRINTERS; i++) {
            PRINTERS[i] = new Printer(i);
        }

        while (true) {
            // 客户端输入一个打印请求
            String printRequest = getInput();

            // 判断打印机的空闲状态
            Printer printer = getFreePrinter();

            if (printer == null) {
                System.out.println("所有打印机都在工作中，请稍后再试！");
                continue;
            }

            // 选择空闲的一台打印机打印
            printer.print(printRequest);

            // 等待三秒
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    private static String getInput() {
        // 假设这里通过控制台输入打印请求
        return "Test Print Request";
    }

    private static Printer getFreePrinter() {
        for (int i = 0; i < NUM_OF_PRINTERS; i++) {
            if (PRINTERS[i].isFree()) {
                return PRINTERS[i];
            }
        }

        return null;
    }
}

class Printer {
    private final int id;
    private boolean isFree;

    public Printer(int id) {
        this.id = id;
        this.isFree = true;
    }

    public synchronized void print(String printRequest) {
        this.isFree = false;
        System.out.println("正在使用打印机 " + this.id + " 打印：" + printRequest);
        this.isFree = true;
    }

    public synchronized boolean isFree() {
        return isFree;
    }
}

以上代码实现了客户端输入打印请求，连接三Joint PDF (Probability Density Function) refers to the probability distribution of two or more random variables. It gives the probability of the occurrence of a particular个打印机，判断打印机的空闲状态，等待三秒，选择空闲的一台打印机打 set of values of these variables.

Mathematically, for two random variables X and Y, the joint PDF f(x,y) is defined as印的功能。其中，`Printer`类表示打印机，`PrinterManager`类表示打印机管理器，负责协调打印机的使用。