Java怎么实现输入一个string表达式然后输出计算的结果

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//算式
public static void test32() throws Exception{
System.out.println("请输入算式：");
Scanner scanner = new Scanner(System.in);
String str = scanner.next("-?\\d*\\.?\\d+[+-/*]-?\\d*\\.?\\d+");
String[] xyStr = str.split("[+-/*]");
float x = Float.parseFloat(xyStr[0]);
float y = Float.parseFloat(xyStr[1]);
float r = 0;
char opt = '+';
if(str.contains("+")){
opt = '+';
r = x + y;
}else if(str.contains("-")){
opt = '-';
r = x - y;
}else if(str.contains("*")){
opt = '*';
r = x * y;
}else if(str.contains("/")){
opt = '/';
r = x / y;
}
System.out.println(x+""+opt+y+"="+r);
}