pi.java

进行RMI调用的实际例子, 远程调用计算PI值的实例, 稍加改造可以实现实际用途

import java.math.*;

public class PI implements Task{
	private static final BigDecimal ZERO = BigDecimal.valueOf(0);
	private static final BigDecimal ONE = BigDecimal.valueOf(1);
	private static final BigDecimal FOUR = BigDecimal.valueOf(4);
	private static final roundingMode = BigDecimal.ROUND_HALF_EVEN;
	private int digits;
	
	public PI(int digits){
		this.digits = digits;
	}
	
	public Object execute(){
		return computePI(digits);
	}
	
	public static BigDecimal computePI(int digits){
		int scale = digits + 5;
		BigDecimal arctan1_5 = arctan(5, scale);
		BigDecimal arctan1_239 = arctan(239, scale);
		BigDecimal pi = arctan1_5.multiply(FOUR).subtract(arctan1_239).multiply(FOUR);
		return pi.setScale(digits, BigDecimal.ROUND_HALF_UP);
	}
	
	public static BigDecimal arctan(int inverseX, int scale){
		BigDecimal result,numer,term;
		BigDecimal invX = BigDecimal.valueOf(inverseX);
		BigDecimal invX2 = BigDecimal.valueOf(inverseX * inverseX);
		numer = ONE.divide(invX, scale, roundingMode);
		result = numer;
		int i = 1;
		do{
			numer = numer.divide(invX2,scale,roundingMode);
			int denom = 2 * i + 1;
			term = numer.divide(BigDecimal.valueOf(denom),scale,roundingMode);
			
			if((i % 2) != 0){
				result = result.subtract(term);
			}else{
				result = result.add(term);
			}
			i++;
		}while(term.compareTo(ZERO) != 0)
		return result;
	}
}