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如何最好地检查字符串输入是否是用于编码的有效 Java 变量？我敢肯定，我不是第一个愿意这样做的人。但也许我错过了正确的关键字来找到有用的东西。

最好的可能是 RegEx，它检查：

  • 以字母开头

  • 然后可以包含数字、字母

  • 可以包含一些特殊字符，例如“_”（哪个？）

  • 可能不包含空格分隔符
4

2 回答 2

20 
public static boolean isValidJavaIdentifier(String s) {
    if (s.isEmpty()) {
        return false;
    }
    if (!Character.isJavaIdentifierStart(s.charAt(0))) {
        return false;
    }
    for (int i = 1; i < s.length(); i++) {
        if (!Character.isJavaIdentifierPart(s.charAt(i))) {
            return false;
        }
    }
    return true;
}

编辑：并且，正如@Joey 所指出的，您还应该过滤掉关键字和保留字。

于 2013-03-15T16:52:12.637 回答
14

Java 6+

采用

import javax.lang.model.SourceVersion;

boolean isValidVariableName(CharSequence name) {
    return SourceVersion.isIdentifier(name) && !SourceVersion.isKeyword(name);
}

如果您需要检查字符串是否是最新版本 Java 中的有效 Java 变量名，或者

import javax.lang.model.SourceVersion;

boolean isValidVariableNameInVersion(CharSequence name, SourceVersion version) {
    return SourceVersion.isIdentifier(name) && !SourceVersion.isKeyword(name, version);
}

如果您需要检查字符串是否是特定Java 版本中的有效 Java 变量名。

例如，下划线从 Java 9 开始成为保留关键字，因此在isValidVariableNameInVersion("_", SourceVersion.RELEASE_9)返回false时isValidVariableNameInVersion("_", SourceVersion.RELEASE_8)返回true。

这个怎么运作

SourceVersion.isIdentifier(CharSequence name)检查 name 在最新源版本中是否是语法上有效的标识符（简单名称）或关键字。!SourceVersion.isKeyword(name)为关键字返回 false。因此，SourceVersion.isIdentifier(name) && !SourceVersion.isKeyword(name)对于有效的标识符返回 true，并且只对它们返回。

内置方法中使用了相同的方法SourceVersion.isName(CharSequence name, SourceVersion version)来检查 name 是否是语法上有效的限定名称，这意味着它将返回true诸如“apple.color”之类的字符串：

public static boolean isName(CharSequence name, SourceVersion version) {
    String id = name.toString();

    for(String s : id.split("\\.", -1)) {
        if (!isIdentifier(s) || isKeyword(s, version))
            return false;
    }
    return true;
}

测试

import org.junit.jupiter.api.Test;

import javax.lang.model.SourceVersion;

import static org.assertj.core.api.Assertions.assertThat;

public class ValidVariableNameTest {
    boolean isValidVariableName(CharSequence name) {
        return isValidVariableNameInVersion(name, SourceVersion.RELEASE_8);
    }

    boolean isValidVariableNameInVersion(CharSequence name, SourceVersion version) {
        return SourceVersion.isIdentifier(name) && !SourceVersion.isKeyword(name, version);
    }

    @Test
    void variableNamesCanBeginWithLetters() {
        assertThat(isValidVariableName("test")).isTrue();
        assertThat(isValidVariableName("e2")).isTrue();
        assertThat(isValidVariableName("w")).isTrue();
        assertThat(isValidVariableName("привет")).isTrue();
    }

    @Test
    void variableNamesCanBeginWithDollarSign() {
        assertThat(isValidVariableName("$test")).isTrue();
        assertThat(isValidVariableName("$e2")).isTrue();
        assertThat(isValidVariableName("$w")).isTrue();
        assertThat(isValidVariableName("$привет")).isTrue();
        assertThat(isValidVariableName("$")).isTrue();
        assertThat(isValidVariableName("$55")).isTrue();
    }

    @Test
    void variableNamesCanBeginWithUnderscore() {
        assertThat(isValidVariableName("_test")).isTrue();
        assertThat(isValidVariableName("_e2")).isTrue();
        assertThat(isValidVariableName("_w")).isTrue();
        assertThat(isValidVariableName("_привет")).isTrue();
        assertThat(isValidVariableName("_55")).isTrue();
    }

    @Test
    void variableNamesCannotContainCharactersThatAreNotLettersOrDigits() {
        assertThat(isValidVariableName("apple.color")).isFalse();
        assertThat(isValidVariableName("my var")).isFalse();
        assertThat(isValidVariableName(" ")).isFalse();
        assertThat(isValidVariableName("apple%color")).isFalse();
        assertThat(isValidVariableName("apple,color")).isFalse();
        assertThat(isValidVariableName(",applecolor")).isFalse();
    }

    @Test
    void variableNamesCannotStartWithDigit() {
        assertThat(isValidVariableName("2e")).isFalse();
        assertThat(isValidVariableName("5")).isFalse();
        assertThat(isValidVariableName("123test")).isFalse();
    }


    @Test
    void differentSourceVersionsAreHandledCorrectly() {
        assertThat(isValidVariableNameInVersion("_", SourceVersion.RELEASE_9)).isFalse();
        assertThat(isValidVariableNameInVersion("_", SourceVersion.RELEASE_8)).isTrue();

        assertThat(isValidVariableNameInVersion("enum", SourceVersion.RELEASE_9)).isFalse();
        assertThat(isValidVariableNameInVersion("enum", SourceVersion.RELEASE_4)).isTrue();
    }

    @Test
    void keywordsCannotBeUsedAsVariableNames() {
        assertThat(isValidVariableName("strictfp")).isFalse();
        assertThat(isValidVariableName("assert")).isFalse();
        assertThat(isValidVariableName("enum")).isFalse();

        // Modifiers
        assertThat(isValidVariableName("public")).isFalse();
        assertThat(isValidVariableName("protected")).isFalse();
        assertThat(isValidVariableName("private")).isFalse();

        assertThat(isValidVariableName("abstract")).isFalse();
        assertThat(isValidVariableName("static")).isFalse();
        assertThat(isValidVariableName("final")).isFalse();

        assertThat(isValidVariableName("transient")).isFalse();
        assertThat(isValidVariableName("volatile")).isFalse();
        assertThat(isValidVariableName("synchronized")).isFalse();

        assertThat(isValidVariableName("native")).isFalse();

        // Declarations
        assertThat(isValidVariableName("class")).isFalse();
        assertThat(isValidVariableName("interface")).isFalse();
        assertThat(isValidVariableName("extends")).isFalse();
        assertThat(isValidVariableName("package")).isFalse();
        assertThat(isValidVariableName("throws")).isFalse();
        assertThat(isValidVariableName("implements")).isFalse();

        // Primitive types and void
        assertThat(isValidVariableName("boolean")).isFalse();
        assertThat(isValidVariableName("byte")).isFalse();
        assertThat(isValidVariableName("char")).isFalse();
        assertThat(isValidVariableName("short")).isFalse();
        assertThat(isValidVariableName("int")).isFalse();
        assertThat(isValidVariableName("long")).isFalse();
        assertThat(isValidVariableName("float")).isFalse();
        assertThat(isValidVariableName("double")).isFalse();
        assertThat(isValidVariableName("void")).isFalse();

        // Control flow
        assertThat(isValidVariableName("if")).isFalse();
        assertThat(isValidVariableName("else")).isFalse();

        assertThat(isValidVariableName("try")).isFalse();
        assertThat(isValidVariableName("catch")).isFalse();
        assertThat(isValidVariableName("finally")).isFalse();

        assertThat(isValidVariableName("do")).isFalse();
        assertThat(isValidVariableName("while")).isFalse();
        assertThat(isValidVariableName("for")).isFalse();
        assertThat(isValidVariableName("continue")).isFalse();

        assertThat(isValidVariableName("switch")).isFalse();
        assertThat(isValidVariableName("case")).isFalse();
        assertThat(isValidVariableName("default")).isFalse();
        assertThat(isValidVariableName("break")).isFalse();
        assertThat(isValidVariableName("throw")).isFalse();

        assertThat(isValidVariableName("return")).isFalse();

        // Other keywords
        assertThat(isValidVariableName("this")).isFalse();
        assertThat(isValidVariableName("new")).isFalse();
        assertThat(isValidVariableName("super")).isFalse();
        assertThat(isValidVariableName("import")).isFalse();
        assertThat(isValidVariableName("instanceof")).isFalse();

        // Reserved keywords
        assertThat(isValidVariableName("goto")).isFalse();
        assertThat(isValidVariableName("const")).isFalse();
    }

    @Test
    void literalsCannotBeUsedAsVariableNames() {
        assertThat(isValidVariableName("null")).isFalse();
        assertThat(isValidVariableName("true")).isFalse();
        assertThat(isValidVariableName("false")).isFalse();
    }
}
于 2015-12-10T14:24:14.070 回答