[英]Java Splitting With Math Expression
我正在嘗試拆分數學表達式。
String number = "100+500";
String[] split = new String[3];
我要實現
我試過這個,但我不知道該寫什么來拆分。
split = number.split(????);
您想在不消耗任何輸入的情況下在數字和非數字之間進行拆分……您需要四處看看:
String[] split = number.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");
正則表達式的火車殘骸到底是什么?
它表達了這個答案的初始句子:
(?<=\\d)
表示前一個字符是數字(?=\\D)
表示下一個字符是非數字(?<=\\d)(?=\\D)
一起將一個數字和一個非數字之間匹配regexA|regexB
表示 regexA或regexB 匹配,用作上面的點,但非數字然后數字用於反邏輯重要的一點是環顧是非消耗性的,因此拆分過程中不會吞噬任何輸入。
下面是一些測試代碼:
String number = "100+500-123/456*789";
String[] split = number.split("(?<=\\d)(?=\\D)|(?<=\\D)(?=\\d)");
System.out.println(Arrays.toString(split));
輸出:
[100, +, 500, -, 123, /, 456, *, 789]
要處理可能有小數點的數字,請使用以下正則表達式:
"(?<=[\\d.])(?=[^\\d.])|(?<=[^\\d.])(?=[\\d.])"
這實際上只是添加.
到作為“數字”的字符。
首先,我不知道拆分的任何庫例程。 自定義拆分例程可能是這樣的:
/**
* Splits the given {@link String} at the operators +, -, * and /
*
* @param string
* the {@link String} to be split.
* @throws NullPointerException
* when the given {@link String} is null.
* @return a {@link List} containing the split string and the operators.
*/
public List<String> split(String string) throws NullPointerException {
if (string == null)
throw new NullPointerException("the given string is null!");
List<String> result = new ArrayList<String>();
// operators to split upon
String[] operators = new String[] { "+", "-", "*", "/" };
int index = 0;
while (index < string.length()) {
// find the index of the nearest operator
int minimum = string.length();
for (String operator : operators) {
int i = string.indexOf(operator, index);
if (i > -1)
minimum = Math.min(minimum, i);
}
// if an operator is found, split the string
if (minimum < string.length()) {
result.add(string.substring(index, minimum));
result.add("" + string.charAt(minimum));
index = minimum + 1;
} else {
result.add(string.substring(index));
break;
}
}
return result;
}
一些測試代碼:
System.out.println(split("100+10*6+3"));
System.out.println(split("100+"));
輸出:
[100, +, 10, *, 6, +, 3]
[100, +]
您還可以在 Java 中使用 Pattern/Matcher 類:
String expression = "100+34";
Pattern p = Pattern.compile("(\\d+)|(\\+)");
Matcher m = p.matcher(expression);
String[] elems = new String[m.groupCount() +1];
int i=0;
while(m.find())
{
elems[i++] = m.group();
}
你可以做一些簡單的事情而不是瘋狂的正則表達式; 只需用空格填充+
:
String number = "100+500";
number = number.replace("+", " + ");
現在您可以在空白處拆分它:
String[] split = number.split(" ");
現在將設置您的索引:
split[0] = "100";
split[1] = "+";
split[2] = "500";
要檢查所有算術符號,如果您希望避免使用正則表達式,可以使用以下方法:
public static String replacing(String s) {
String[] chars = {"+", "-", "/", "="};
for (String character : chars) {
if (s.contains(character)) {
s = s.replace(character, " " + character + " ");//not exactly elegant, but it works
}
}
return s;
}
//in main method
number = replacing(number);
String[] split = number.split(" ");
您可以拆分表達式字符串,然后得到純標記和分類標記。 mXparser庫支持此以及計算過程。 請按照以下示例操作:
你非常簡單的例子“100+500”:
import org.mariuszgromada.math.mxparser.*;
...
...
Expression e = new Expression("100+500");
mXparser.consolePrintTokens( e.getCopyOfInitialTokens() );
結果:
[mXparser-v.4.0.0] --------------------
[mXparser-v.4.0.0] | Expression tokens: |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] | TokenIdx | Token | KeyW | TokenId | TokenTypeId | TokenLevel | TokenValue | LooksLike |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] | 0 | 100 | _num_ | 1 | 0 | 0 | 100.0 | |
[mXparser-v.4.0.0] | 1 | + | + | 1 | 1 | 0 | NaN | |
[mXparser-v.4.0.0] | 2 | 500 | _num_ | 1 | 0 | 0 | 500.0 | |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
更復雜的例子“2*sin(x)+(3/cos(y)-e^(sin(x)+y))+10”:
import org.mariuszgromada.math.mxparser.*;
...
...
Argument x = new Argument("x");
Argument y = new Argument("y");
Expression e = new Expression("2*sin(x)+(3/cos(y)-e^(sin(x)+y))+10", x, y);
mXparser.consolePrintTokens( e.getCopyOfInitialTokens() );
結果:
[mXparser-v.4.0.0] --------------------
[mXparser-v.4.0.0] | Expression tokens: |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] | TokenIdx | Token | KeyW | TokenId | TokenTypeId | TokenLevel | TokenValue | LooksLike |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
[mXparser-v.4.0.0] | 0 | 2 | _num_ | 1 | 0 | 0 | 2.0 | |
[mXparser-v.4.0.0] | 1 | * | * | 3 | 1 | 0 | NaN | |
[mXparser-v.4.0.0] | 2 | sin | sin | 1 | 4 | 1 | NaN | |
[mXparser-v.4.0.0] | 3 | ( | ( | 1 | 20 | 2 | NaN | |
[mXparser-v.4.0.0] | 4 | x | x | 0 | 101 | 2 | NaN | |
[mXparser-v.4.0.0] | 5 | ) | ) | 2 | 20 | 2 | NaN | |
[mXparser-v.4.0.0] | 6 | + | + | 1 | 1 | 0 | NaN | |
[mXparser-v.4.0.0] | 7 | ( | ( | 1 | 20 | 1 | NaN | |
[mXparser-v.4.0.0] | 8 | 3 | _num_ | 1 | 0 | 1 | 3.0 | |
[mXparser-v.4.0.0] | 9 | / | / | 4 | 1 | 1 | NaN | |
[mXparser-v.4.0.0] | 10 | cos | cos | 2 | 4 | 2 | NaN | |
[mXparser-v.4.0.0] | 11 | ( | ( | 1 | 20 | 3 | NaN | |
[mXparser-v.4.0.0] | 12 | y | y | 1 | 101 | 3 | NaN | |
[mXparser-v.4.0.0] | 13 | ) | ) | 2 | 20 | 3 | NaN | |
[mXparser-v.4.0.0] | 14 | - | - | 2 | 1 | 1 | NaN | |
[mXparser-v.4.0.0] | 15 | e | e | 2 | 9 | 1 | NaN | |
[mXparser-v.4.0.0] | 16 | ^ | ^ | 5 | 1 | 1 | NaN | |
[mXparser-v.4.0.0] | 17 | ( | ( | 1 | 20 | 2 | NaN | |
[mXparser-v.4.0.0] | 18 | sin | sin | 1 | 4 | 3 | NaN | |
[mXparser-v.4.0.0] | 19 | ( | ( | 1 | 20 | 4 | NaN | |
[mXparser-v.4.0.0] | 20 | x | x | 0 | 101 | 4 | NaN | |
[mXparser-v.4.0.0] | 21 | ) | ) | 2 | 20 | 4 | NaN | |
[mXparser-v.4.0.0] | 22 | + | + | 1 | 1 | 2 | NaN | |
[mXparser-v.4.0.0] | 23 | y | y | 1 | 101 | 2 | NaN | |
[mXparser-v.4.0.0] | 24 | ) | ) | 2 | 20 | 2 | NaN | |
[mXparser-v.4.0.0] | 25 | ) | ) | 2 | 20 | 1 | NaN | |
[mXparser-v.4.0.0] | 26 | + | + | 1 | 1 | 0 | NaN | |
[mXparser-v.4.0.0] | 27 | 10 | _num_ | 1 | 0 | 0 | 10.0 | |
[mXparser-v.4.0.0] ---------------------------------------------------------------------------------------------------------------
要了解 Token.tokenId 和 Token.tokenTypeId 的含義,您需要參考API 文檔和解析器部分。 例如在 Operator 類中,您有
請遵循mXparser 教程以獲得更好的理解。
此致
由於 +,-,* 基本上所有數學符號都是特殊字符,因此您可以像這樣在 split 函數中在它們之前放置一個“\\\\”
String number = "100+500";
String[] numbers = number.split("\\+");
for (String n:numbers) {
System.out.println(n);
}
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