我刚开始使用Java，并且不知道如何调用该类并使用正确的变量。我有一个Calculator.java文件，其中我有读取2 int，添加或乘以它们的方法。 （最后粘贴它们）
Calculator.java
class Calculator {
int x;
int y;
public setNumbers(int x, int y) {
System.out.print("Input the first number: ");
return x = in.nextInt();
System.out.print("Input the second number: ");
return y = in.nextInt();
}
public addNumbers(){
return x + y;
}
public multiplyNumbers(){
return x * y;
}
}
CalculatorApp.java
class CalculatorApp extends Calculator {
public int pr() {
return pr();
}
public static void main(String[] args) {
int choice;
System.out.println("Please choose one of the following options: \n[1] - Set numbers \n[2] - Add Numbers \n[3] - Multiply numbers \nYour choice is: ");
choice = in.nextInt();
switch (choice) {
case 1: setNumbers();
break;
case 2: addNumbers();
break;
case 3: multiplyNumbers();
break;
}
}
}
错误：
.\Calculator.java:6: error: invalid method declaration; return type required
public setNumbers(int x, int y) {
^
.\Calculator.java:15: error: invalid method declaration; return type required
public addNumbers(){
^
.\Calculator.java:21: error: invalid method declaration; return type required
public multiplyNumbers(){
^
.\Calculator.java:9: error: incompatible types: unexpected return value
return x = in.nextInt();
^
.\Calculator.java:9: error: cannot find symbol
return x = in.nextInt();
^
symbol: variable in
location: class Calculator
.\Calculator.java:11: error: incompatible types: unexpected return value
return y = in.nextInt();
^
.\Calculator.java:11: error: cannot find symbol
return y = in.nextInt();
^
symbol: variable in
location: class Calculator
.\Calculator.java:17: error: incompatible types: unexpected return value
return x + y;
^
.\Calculator.java:23: error: incompatible types: unexpected return value
return x * y;
^
CalculatorApp.java:12: error: cannot find symbol
choice = in.nextInt();
^
symbol: variable in
location: class CalculatorApp
CalculatorApp.java:16: error: cannot find symbol
case 1: setNumbers();
^
symbol: method setNumbers()
location: class CalculatorApp
CalculatorApp.java:19: error: cannot find symbol
case 2: addNumbers();
^
symbol: method addNumbers()
location: class CalculatorApp
CalculatorApp.java:22: error: cannot find symbol
case 3: multiplyNumbers();
^
symbol: method multiplyNumbers()
location: class CalculatorApp
13 errors
答案 0 :(得分：0)
java中的每个函数都需要一个返回类型，它是一个方法在返回一个整数值时返回的值，返回类型是int，如果一个floting值则返回类型是float。
另请注意，您已使用in.nextInt（）; 这也是错误的你必须使用扫描仪来输入。 此外，setNumbers方法接受两个不需要的参数，因为您只从方法中的用户获取数字。 我认为这些行
public int pr() {
return pr();
}
毫无意义。
答案 1 :(得分：0)
我认为在您的Calculator类中，您的函数缺少从函数返回值的返回类型。
你的计算器类可能是这样的。
class Calculator {
int x;
int y;
public void setNumbers() {
System.out.print("Input the first number: ");
Scanner in = new Scanner(System.in);
this.x = in.nextInt();
System.out.print("Input the second number: ");
this.y = in.nextInt();
}
public int addNumbers(){
return this.x + this.y;
}
public int multiplyNumbers(){
return this.x * this.y;
}
}
另外使用＆＃34; Scanner in = new Scanner（System.in）; ＆＃34;在主要功能。
答案 2 :(得分：0)
使用以下代码。如果您希望我解释一些基本的理解，请在下面写下评论。
Calculator.java
public class Calculator {
int x;
int y;
public void setNumbers(int x, int y) {
this.x = x;
this.y = y;
}
public int addNumbers(){
return x + y;
}
public int multiplyNumbers(){
return x * y;
}
}
CalculatorApp.java
import java.util.Scanner;
public class CalculatorApp {
public static void main(String[] args) {
int choice;
Scanner in = new Scanner(System.in);
Calculator calculator = new Calculator();
while(true) {
System.out.println("Please choose one of the following options: \n[1] - Set numbers \n[2] - Add Numbers \n[3] - Multiply numbers \n[4] - Exit\nYour choice is: ");
choice = in.nextInt();
switch (choice) {
case 1:
System.out.print("\nInput the first number: ");
int x = in.nextInt();
System.out.print("\nInput the second number: ");
int y = in.nextInt();
calculator.setNumbers(x, y);
break;
case 2:
int sum = calculator.addNumbers();
System.out.println("Sum: " + sum);
break;
case 3:
int multiply = calculator.multiplyNumbers();
System.out.println("Multiply: " + multiply);
break;
default:
System.exit(0);
}
}
}
}
编译 javac Calculator.java ，而不是 javac CalculatorApp.java 。并运行 java CalculatorApp
答案 3 :(得分：0)
所以这里有完整的代码可能有效
class Calculator {
int x;
int y;
public void setNumbers() {
System.out.print("Input the first number: ");
x = in.nextInt();
System.out.print("Input the second number: ");
y = in.nextInt();
}
public int addNumbers(){
return x + y;
}
public int multiplyNumbers(){
return x * y;
}
}
和班级计算器应用
class CalculatorApp extends Calculator {
public int pr() {
return pr();
}
public static void main(String[] args) {
java.util.Scanner sc =new Scanner(System.in);
int choice;
//note you have to setnumbers before you could add or multiply them
System.out.println("Press 1 to add numbers");
Syste.out.print("Press 2 to multiply numbers");
choice = sc.nextInt();
setNumbers();
switch (choice) {
case 1:
system.out.print( addNumbers());
break;
case 2:
System.out.print( multiplyNumbers());
break;
default:
S.op.ln("Invalid choice");
}
}
}
答案 4 :(得分：0)
public class Calculator {
int x;
int y;
public void setNumbers() {
Scanner sc = new Scanner(System.in);
System.out.print("Input the first number: ");
this.x = sc.nextInt();
System.out.print("Input the second number: ");
this.y = sc.nextInt();
}
public int addNumbers(){
return this.x + this.y;
}
public int multiplyNumbers(){
return this.x * this.y;
}
}
public class CalculatorApp{
public int pr() {
return pr();
}
public static void main(String[] args) {
Calculator cal = new Calculator();
int choice;
Scanner sc = new Scanner(System.in);
System.out.println("Please choose one of the following options: \n[1] - Add Numbers \n[2] - Multiply numbers \nYour choice is: ");
choice = sc.nextInt();
switch (choice) {
case 1:
cal.setNumbers();
System.out.println(cal.addNumbers());
break;
case 2:
cal.setNumbers();
System.out.println(cal.multiplyNumbers());
break;
}
}
}