Effective Java 第十五条：使可变性最小化

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复数类Complex：

public final class Complex {    private final double re;    private final double im;    public Complex(double im, double re) {        this.im = im;        this.re = re;    }    public double realPart(){        return im;    }    public double imaginaryPart(){        return re;    }    public Complex add(Complex c){        return new Complex(re + c.re, im + c.im);    }    public Complex subtract(Complex c){        return new Complex(re - c.re, im - c.im);    }    public Complex motiply(Complex c){        return new Complex(re * c.re - im * c.im, re * c.re + im * c.im);    }    public Complex divide(Complex c){        double temp = im * c.im + re * c.re;        return new Complex((re * c.re + im * c.im) / temp, (re * c.re - im * c.im) / temp);    }    @Override    public int hashCode() {        int result = 17 + hashDouble(re);        result = 31 * result + hashDouble(im);        return result;    }    private int hashDouble(double val){        long longBits = Double.doubleToLongBits(val);        return (int)(longBits ^ (longBits >>> 32));    }    @Override    public boolean equals(Object obj) {        if(obj == this)            return true;        if(!(obj instanceof Complex))            return false;        Complex c = (Complex) obj;        return Double.compare(im, c.im) == 0 &&                Double.compare(re , c.re) == 0;    }    @Override    public String toString() {        return "+ re + " + re +" + im + " + im;    }}

测试：

public class ComplexText {    public static void main(String[] args) {        Complex complex = new Complex(1.0,2.0);        Complex complex1 = new Complex(2.0,3.0);        System.out.println(complex.add(complex1));        System.out.println(complex.divide(complex1));        System.out.println(complex.subtract(complex1));        System.out.println(complex.motiply(complex1));    }}

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