试图在Java中操作字符串并不断获取“布尔值”

我在Eclipse中编写代码，因此我的一些错误消息可能会有所不同。我正在尝试打印一条消息，以便在字符串s3中没有字符“a”时，它会告诉用户尝试另一行代码。我语句的if部分没有问题，但else部分有问题。我似乎无法确定如何修复我的语句，因此如果ne可以帮忙，谢谢

//print the index of the last occurrence of the character 'a' in string s3
if (s3.indexOf('a')>= 0 {
System.out.println("The first occurrence of the character 'a' in both strings is at index " + s3.indexOf('a'));
}
else (s3.indexOf('a') > 0 )
System.out.println("There is no occurrence of the character 'a' in either string.");
}

您的else在第二次测试中缺少else if。这是无效的，并且在第一次if测试中无法访问您在那里设置的条件。您可以使用else。类似

if (s3.indexOf('a')>= 0 {
    System.out.println("The first occurrence of the character 'a' "
            + "in both strings is at index " + s3.indexOf('a'));
} else {
    System.out.println("There is no occurrence of the character 'a' "
            + "in either string.");
}

或改变

到

使用elseif语句

if(s3.indexOf('a')>= 0     {
    System.out.println("The first occurrence of the character 'a' in both strings is at index " + s3.indexOf('a'));
}
else if (s3.indexOf('a') < 0 )
    System.out.println("There is no occurrence of the character 'a' in either string.");
}

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当if表达式的计算结果为false时，if-then-else语句提供了执行的辅助路径。因此，在else子句中，您不需要条件

if (s3.indexOf('a')>= 0 {
    System.out.println("The first occurrence of the character 'a' in both strings is at index " + s3.indexOf('a'));
} else {
    System.out.println("There is no occurrence of the character 'a' in either string.");
}

而else子句中缺少了开头大括号。

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有关更多信息，您可以阅读

，只需使用else即可

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如果第二个else包含相同的条件，则第二个else与第一个else不可访问

首先在第一行添加一个右括号，这样代码将编译。

if(s3.indexOf('a')>= 0     {
    System.out.println("The first occurrence of the character 'a' in both strings is at index " + s3.indexOf('a'));
}
else if (s3.indexOf('a') < 0 )
    System.out.println("There is no occurrence of the character 'a' in either string.");
}

if (s3.indexOf('a')>= 0 {
    System.out.println("The first occurrence of the character 'a' in both strings is at index " + s3.indexOf('a'));
} else {
    System.out.println("There is no occurrence of the character 'a' in either string.");
}