Java - 错误消息：'无法从 void 转换为 String
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Java - Error Message: 'Cannot Convert from void to String
提问by Joel Biffin
I am creating a simple console applet for an assignment and I have ran into an error when trying to run my app. The error is:
'Type mismatch: cannot convert from void to String'.
我正在为一项任务创建一个简单的控制台小程序，但在尝试运行我的应用程序时遇到了错误。错误是：
“类型不匹配：无法从 void 转换为 String”。
The error occurs four times as I have a recurring 'ElseIf' statement.
Here is the element where the problem is:
该错误出现四次，因为我有一个重复的“ElseIf”语句。
这是问题所在的元素：
String thirdNum = println("Would you like a third number?(Y/N)");
Here is the complete code:
这是完整的代码：
import acm.program.*;
public class abacusConsole extends ConsoleProgram {
public void run() {
println("This program is a basic calculator two numbers!");
println("Operations that the program recognises: \n Add \n Subtract \n Multiply \n Divide");
String operator = readLine("Which operator would you like to use?");
if (operator.equals("Add")) {
int n1 = readInt("First Number");
int n2 = readInt("Second Number");
String thirdNum = println("Would you like a third number?(Y/N)");
if (thirdNum.equals("Y")) {
int n3 = readInt("Third Number:");
int total = n1 + n2 + n3;
println(+n1+" + "+n2+" + "+n3+" = "+total+".");
} else if (thirdNum.equals("N")) {
int total = n1 + n2;
println(+n1+" + "+n2+" = "+total+".");
} else {
println("Please reload the application and type in either 'Y' or 'N'");
}
} else if (operator.equals("Subtract")) {
int n1 = readInt("First Number");
int n2 = readInt("Second Number");
String thirdNum = println("Would you like a third number?(Y/N)");
if (thirdNum.equals("Y")) {
int n3 = readInt("Third Number:");
int total = n1 - n2 - n3;
println(+n1+" - "+n2+" - "+n3+" = "+total+".");
} else if (thirdNum.equals("N")) {
int total = n1 + n2;
println(+n1+" - "+n2+" = "+total+".");
} else {
println("Please reload the application and type in either 'Y' or 'N'");
}
} else if (operator.equals("Multiply")) {
int n1 = readInt("First Number");
int n2 = readInt("Second Number");
String thirdNum = println("Would you like a third number?(Y/N)");
if (thirdNum.equals("Y")) {
int n3 = readInt("Third Number:");
int total = n1 * n2 * n3;
println(+n1+" x "+n2+" x "+n3+" = "+total+".");
} else if (thirdNum.equals("N")) {
int total = n1 * n2;
println(+n1+" x "+n2+" = "+total+".");
} else {
println("Please reload the application and type in either 'Y' or 'N'");
}
} else if (operator.equals("Divide")) {
int n1 = readInt("First Number");
int n2 = readInt("Second Number");
String thirdNum = println("Would you like a third number?(Y/N)");
if (thirdNum.equals("Y")) {
int n3 = readInt("Third Number:");
int total = n1 / n2 / n3;
println(+n1+" / "+n2+" / "+n3+" = "+total+".");
} else if (thirdNum.equals("N")) {
int total = n1 / n2;
println(+n1+" / "+n2+" = "+total+".");
} else {
println("Please reload the application and type in either 'Y' or 'N'");
}
}
}
}
回答by La bla bla
looking at this line of your code
看看你的这行代码
String operator = readLine("Which operator would you like to use?");`
and comparing it with the one which causes the error
并将其与导致错误的那个进行比较
String thirdNum = println("Would you like a third number?(Y/N)");
It looks like you misplaced readLinewith println
看起来你放错readLine了地方println
回答by Kai Mattern
String thirdNum = println("Would you like a third number?(Y/N)");
println or (printline) does exactly that. It prints a line and returns nothing. You try to put that nothing (void) into a string. That does not work.
println 或 (printline) 正是这样做的。它打印一行并且不返回任何内容。您尝试将任何内容（空）放入字符串中。那行不通。
You probably meant to use another
你可能打算使用另一个
readline
回答by dbf
Looks like your println function is declared as void (please post it's signature btw), but you are trying to assing it's result (void) to a String variable.
看起来您的 println 函数被声明为 void（顺便说一下，请张贴它的签名），但是您正试图将它的结果 (void) 分配给 String 变量。
回答by Juvanis
println()method has no return type, so it returns voidand you cannot assign it to a Stringreference obviously.
println()方法没有返回类型，因此它返回void并且您String显然不能将其分配给引用。
