java编程序： 实现一个复数类Complex, 成员函数包括加、减、乘、除、打印、返回实部、虚部 和 toString()方法等， 其中toString（）返回 a+bi形式的字符串。 成员函数：Add/Sub/Multiply/Divide不修改对象值，而是返回一个新对象。

在Java中，我们可以创建一个名为`Complex`的类来表示复数，并提供你所提到的各种成员函数。这是一个简单的例子：

public class Complex {
    private double real;
    private double imaginary;

    // 构造函数，初始化复数的实部和虚部
    public Complex(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }

    // 获取实部和虚部
    public double getReal() {
        return real;
    }
    
    public double getImaginary() {
        return imaginary;
    }

    // 加法，返回一个新的复数对象
    public Complex add(Complex other) {
        double newReal = this.real + other.getReal();
        double newImaginary = this.imaginary + other.getImaginary();
        return new Complex(newReal, newImaginary);
    }

    // 减法，返回一个新的复数对象
    public Complex subtract(Complex other) {
        double newReal = this.real - other.getReal();
        double newImaginary = this.imaginary - other.getImaginary();
        return new Complex(newReal, newImaginary);
    }

    // 乘法，返回一个新的复数对象
    public Complex multiply(Complex other) {
        double newReal = this.real * other.getReal() - this.imaginary * other.getImaginary();
        double newImaginary = this.real * other.getImaginary() + this.imaginary * other.getReal();
        return new Complex(newReal, newImaginary);
    }

    // 除法，返回一个新的复数对象（假设除数非零）
    public Complex divide(Complex divisor) {
        double denominator = divisor.getReal() * divisor.getReal() + divisor.getImaginary() * divisor.getImaginary();
        double newReal = (this.real * divisor.getReal() + this.imaginary * divisor.getImaginary()) / denominator;
        double newImaginary = (this.imaginary * divisor.getReal() - this.real * divisor.getImaginary()) / denominator;
        return new Complex(newReal, newImaginary);
    }

    // 打印复数，如"a + bi"的形式
    @Override
    public String toString() {
        if (imaginary >= 0) {
            return real + " + " + imaginary + "i";
        } else {
            return real + " - " + (-imaginary) + "i";
        }
    }
}

在这个类中，所有的操作都不会直接修改对象的状态，而是通过返回新的`Complex`实例来体现复数运算的特性。