用Java声明并测试一个复数类,其方法包括 toString()及复数的加、减、乘运算

可以使用Java声明并测试一个复数类，如下所示：

public class ComplexNumber {
    private double real;
    private double imaginary;
    
    public ComplexNumber(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }
    
    public String toString() {
        if (imaginary < 0) {
            return real + " - " + Math.abs(imaginary) + "i";
        } else {
            return real + " + " + imaginary + "i";
        }
    }
    
    public ComplexNumber add(ComplexNumber other) {
        double newReal = this.real + other.real;
        double newImaginary = this.imaginary + other.imaginary;
        return new ComplexNumber(newReal, newImaginary);
    }
    
    public ComplexNumber subtract(ComplexNumber other) {
        double newReal = this.real - other.real;
        double newImaginary = this.imaginary - other.imaginary;
        return new ComplexNumber(newReal, newImaginary);
    }
    
    public ComplexNumber multiply(ComplexNumber other) {
        double newReal = this.real * other.real - this.imaginary * other.imaginary;
        double newImaginary = this.real * other.imaginary + this.imaginary * other.real;
        return new ComplexNumber(newReal, newImaginary);
    }
}

使用上述复数类进行测试的示例代码如下：

public class Main {
    public static void main(String[] args) {
        ComplexNumber num1 = new ComplexNumber(3, 2);
        ComplexNumber num2 = new ComplexNumber(1, -1);
        
        System.out.println("num1: " + num1.toString());
        System.out.println("num2: " + num2.toString());
        
        ComplexNumber sum = num1.add(num2);
        ComplexNumber difference = num1.subtract(num2);
        ComplexNumber product = num1.multiply(num2);
        
        System.out.println("Sum: " + sum.toString());
        System.out.println("Difference: " + difference.toString());
        System.out.println("Product: " + product.toString());
    }
}

输出结果：

num1: 3.0 + 2.0i
num2: 1.0 - 1.0i
Sum: 4.0 + 1.0i
Difference: 2.0 + 3.0i
Product: 5.0 + 1.0i