如何在 switch 语句默认情况下用 System.out.print() 替换抛出异常

Question

这里我有一个简单的class来进行计算器运算

Calculator.java

    private final ArrayList <Double> values;
    private final String operation;

    public Calculator(ArrayList<Double> values, String operation) {
        this.values = values;
        this.operation = operation;
    }

    public double calculate(){
        double num1 = values.get(0);
        double num2 = values.get(1);
        double answer;

        switch (operation) {
            case "+" :
                answer = addition(num1,num2);
                break;
            case "-" :
                answer = subtraction(num1,num2);
                break;
            case "*" :
                answer = multiplication(num1,num2);
                break;
            case "/" :
                answer = division(num1,num2);
                break;
            default:
                throw new IllegalStateException("Unexpected value: " + operation);
        }
        return answer;
    }

    public double addition(double num1,double num2){
        return num1+num2;
    }
    public double subtraction(double num1,double num2){
        return num1-num2;
    }
    public double multiplication(double num1,double num2){
        return num1*num2;
    }
    public double division(double num1,double num2){
        return num1/num2;
    }
}

这里我要替换throw new IllegalStateException("Unexpected value: " + operation); 这个有我自己的 System.out 消息和 return 什么都没有并停止程序执行。

这里我不能用return 0因为这是一个计算器

其实我想知道如何在没有红色字母异常消息的情况下使用我自己的系统输出语句在 cli 中正确处理此异常。

我这里用的是JDK14

Answer 1

[...] and return noting and stop program execution.

由于方法签名的 return 类型 double 您必须 return 结果。你不能 return 没有结果。

为此，您可以更改方法契约并使 return 类型的 calculate 方法成为 void 并通过单独的方法访问计算结果。

private final ArrayList <Double> values;
private final String operation;
private Double result; //an instance variable to store the result.

public void calculate() {
    Double num1 = values.get(0);
    Double num2 = values.get(1);
    switch (operation) {
        case "+" :
            result = addition(num1,num2);
            break;
        case "-" :
            result = subtraction(num1,num2);
            break;
        case "*" :
            result = multiplication(num1,num2);
            break;
        case "/" :
            result = division(num1,num2);
            break;
        default:
           //Your print statement here
    }
 }

public Optional<Double> getResult() {
    return Optional.ofNullable(result);
}

当呼叫者在 calculate 之前呼叫 getResult() 时会发生这种情况的问题。我会把它留给你。

如何在 switch 语句默认情况下用 System.out.print() 替换抛出异常

How can I replace throw exception with a System.out.print() in switch statement default case

java

exception

switch-statement

java-14