我假设这是一个字符串，你正在试图操作。例如“10. 5 +6* 7. 0”。我将假设你正在存储用户输入在一个字符串构建器。
每次用户输入字符时，您都会将其附加到StringBuilder中。始终跟踪字符串中最右边的“数字分隔符”。分隔符示例：+-*/%（）[]。您知道当前键入的数字从最右边的分隔符之后开始。请检查从分隔符到字符串长度的字符，以查看数字中是否已有小数。

import java.util.*;
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;

class Foo {
    int rightmostDelimiterIdx = 0;
    List<Character> delimiters = Arrays.asList('+', '-', '*', '/', '%', '(', ')', '[', ']');
    
    public static void main(String[] args){
        Foo foo = new Foo();
        try {
            foo.run();
        } catch (ScriptException e) {
            e.printStackTrace();
        }
    }
    
    public void run() throws ScriptException
    {
        StringBuilder sb = new StringBuilder(); // store user input
        ScriptEngineManager mgr = new ScriptEngineManager(); // evaluate expression with JavaScript
        ScriptEngine engine = mgr.getEngineByName("JavaScript");
        
        // User types:5.0*7
        charTyped(sb, '5');
        charTyped(sb,'.');
        charTyped(sb,'0');
        charTyped(sb,'*');
        charTyped(sb,'7');
        System.out.println(engine.eval(sb.toString()));
        sb.setLength(0);
        // User types:8+2.3.3
        charTyped(sb, '8');
        charTyped(sb,'+');
        charTyped(sb,'2');
        charTyped(sb,'.');
        charTyped(sb,'3');
        charTyped(sb,'.'); // second decimal will be rejected, thus string will be "8+2.33"
        charTyped(sb,'3');
        System.out.println(engine.eval(sb.toString()));
    }
    
    // appends c to sb if valid operation
    public void charTyped(StringBuilder sb, char c)
    {
        if(delimiters.contains(c)) {
            rightmostDelimiterIdx = sb.length();
        } else if(c == '.' && sb.indexOf(".", rightmostDelimiterIdx) != -1) {
            return; // do not add '.' b/c already exists in number
        }
        
        sb.append(c);
    }
    
    public void charDeleted(StringBuilder sb, char c) {
        // I leave implementation up to you
    }
}

输出：
35.0
10.33