primefinder.java

来自「21天学通JAVA2（第三版）（专业参考版）」· Java 代码 · 共 37 行

public class PrimeFinder implements Runnable {
    public long target;
    public long prime;
    public boolean finished = false;
    private Thread runner;

    PrimeFinder(long inTarget) {
        target = inTarget;
        if (runner == null) {
            runner = new Thread(this);
            runner.start();
        }
    }
 
    public void run() {
        long numPrimes = 0;
        long candidate = 2;
        while (numPrimes < target) {
            if (isPrime(candidate)) {
                numPrimes++;
                prime = candidate;
            }
            candidate++;
        }
        finished = true;
    }

    boolean isPrime(long checkNumber) {
        double root = Math.sqrt(checkNumber); 
        for (int i = 2; i <= root; i++) {
            if (checkNumber % i == 0)
                return false;
        }
        return true;
    }
}