一个简单的计算器代码（Java）的问题

Question

所以我一直在尝试自己用Java制作一个简单的计算器程序，但我似乎遇到了问题。该代码似乎没有错误（在 Eclipse 或命令提示符中均未显示），但是当我运行它时，它会在您输入操作后结束。这是我的代码示例：

public class vjezba1
{
public static void main(String[] args)
{
Scanner input=new Scanner(System.in);
Scanner text=new Scanner(System.in);

String opr;
int x;
int y;
int sum;

System.out.println("This is a simple calculator program.");
System.out.println("Input first number: ");
x = input.nextInt();

System.out.println("Input second number: ");
y = input.nextInt();

System.out.println("Choose an operation (+,-,*,/): ");
opr = text.nextLine();

if(opr == "+"){
    sum = x + y;
    System.out.println("Result is: " + sum);
}else if(opr == "-"){
    sum = x - y;
    System.out.println("Result is: " + sum);
}else if(opr == "*"){
    sum = x * y;
    System.out.println("Result is: " + sum);
}else if(opr == "/"){
    sum = x / y;
    System.out.println("Result is: " + sum);
}

}
}

感谢任何和所有见解。

Answer 1

使用方法

string.equals("字符串")

在 Java 中比较两个字符串时

类的名称也以大写字母开头，这是一种编程约定。

http://www.oracle.com/technetwork/java/codeconventions-135099.html

import java.io.*;
import java.util.Scanner;

public class Vjezba1
{
public static void main(String[] args)
{
Scanner input=new Scanner(System.in);
Scanner text=new Scanner(System.in);

String opr;
int x;
int y;
int sum;

System.out.println("This is a simple calculator program.");
System.out.println("Input first number: ");
x = input.nextInt();

System.out.println("Input second number: ");
y = input.nextInt();

System.out.println("Choose an operation (+,-,*,/): ");
opr = text.nextLine();
System.out.print(opr);
if(opr.equals("+")){
    sum = x + y;
    System.out.println("Result is: " + sum);
}else if(opr.equals("-")){
    sum = x - y;
    System.out.println("Result is: " + sum);
}else if(opr.equals("*")){
    sum = x * y;
    System.out.println("Result is: " + sum);
}else if(opr.equals("/")){
    sum = x / y;
    System.out.println("Result is: " + sum);
}

}
}