java，从键盘上输入复数并进行判断输入的合法性，并进行加减法，结果打印输出

以下是一个简单的Java代码实现，可以实现输入复数、判断输入合法性、复数的加减法运算以及打印输出结果：

import java.util.Scanner;

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

    public ComplexNumber(double real, double imaginary) {
        this.real = real;
        this.imaginary = imaginary;
    }

    public double getReal() {
        return real;
    }

    public double getImaginary() {
        return imaginary;
    }

    public ComplexNumber add(ComplexNumber other) {
        double real = this.real + other.real;
        double imaginary = this.imaginary + other.imaginary;
        return new ComplexNumber(real, imaginary);
    }

    public ComplexNumber subtract(ComplexNumber other) {
        double real = this.real - other.real;
        double imaginary = this.imaginary - other.imaginary;
        return new ComplexNumber(real, imaginary);
    }

    public String toString() {
        if (imaginary >= 0) {
            return real + " + " + imaginary + "i";
        } else {
            return real + " - " + (-imaginary) + "i";
        }
    }

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.print("请输入第一个复数的实部和虚部（用空格隔开）：");
        double real1 = scanner.nextDouble();
        double imaginary1 = scanner.nextDouble();
        ComplexNumber c1 = new ComplexNumber(real1, imaginary1);

        System.out.print("请输入第二个复数的实部和虚部（用空格隔开）：");
        double real2 = scanner.nextDouble();
        double imaginary2 = scanner.nextDouble();
        ComplexNumber c2 = new ComplexNumber(real2, imaginary2);

        System.out.println("您输入的两个复数分别为：" + c1.toString() + "，" + c2.toString());

        // 判断输入合法性
        if (Double.isNaN(real1) || Double.isNaN(imaginary1) || Double.isNaN(real2) || Double.isNaN(imaginary2)) {
            System.out.println("您输入的复数不合法！");
            return;
        }

        // 复数加减法运算
        ComplexNumber sum = c1.add(c2);
        ComplexNumber difference = c1.subtract(c2);

        // 打印输出结果
        System.out.println("两个复数的和为：" + sum.toString());
        System.out.println("两个复数的差为：" + difference.toString());
    }
}

在main方法中，首先通过Scanner类从键盘上读取两个复数的实部和虚部，并用ComplexNumber类的构造函数创建对应的ComplexNumber对象。接着判断输入的实部和虚部是否为NaN，如果是，则说明输入的复数不合法，直接输出错误信息并退出程序；否则，进行复数的加减法运算，并通过toString方法将结果转化为字符串输出到屏幕上。