Question

我正在收到用户输入并检查句子中是否有“java”这个词。我做了一个while循环，但即使单词'java'在句子中，它也告诉我它不是并继续while循环。如果我删除while循环，我希望程序执行的所有其他操作。这是代码：

import java.util.Scanner;

    public class Main {

    public static void main(String[] args) {

        //declare all variables
        String sentence;
        int java_index_number;
        String stop_program;
        String java;
        String Java;
        String JAVA;
        String java_capital_first_letter;
        String java_all_caps;

        //scanner to get user input
        Scanner user_input = new Scanner(System.in);

        //prompt the user for a sentence
        System.out.print("Enter a line of text containing the word 'java' somewhere within it: ");
        sentence = user_input.nextLine();

        java = "java";
        Java = "Java";
        JAVA = "JAVA";
        while(!sentence.contains(java) || !sentence.contains(Java) || !sentence.contains(JAVA)) {
            System.out.println("Your sentence does not have the word 'java' within it.");
            System.out.print("Enter a line of text containing the word 'java' somewhere within it: ");
            sentence = user_input.nextLine();
        }

        //output
        System.out.println();
        System.out.println("The string read is: " + sentence);
        System.out.println("Length in chars is: " + sentence.length());
        System.out.println("All lowercase is: " + sentence.toLowerCase());
        System.out.println("All uppercase is is: " + sentence.toUpperCase());

        //store java index pos in variable
        java_index_number = sentence.indexOf("java");
        System.out.println("Found 'java' or at pos: " + java_index_number);


        //make first letter of java a capital letter
        java_capital_first_letter = sentence.substring(0, java_index_number) + sentence.substring(java_index_number,
                java_index_number + 1).toUpperCase() + sentence.substring(java_index_number + 1, java_index_number + 4)
                + sentence.substring(java_index_number + 4);

        //make java all caps
        java_all_caps = sentence.substring(0, java_index_number) + sentence.substring(java_index_number,
                java_index_number + 4).toUpperCase() + sentence.substring(java_index_number + 4);

        //output
        System.out.println("Changing to 'Java': " + java_capital_first_letter);
        System.out.println("Changing to 'JAVA': " + java_all_caps);

        // Keep console window alive until 'enter' pressed
        System.out.println();
        System.out.println("Done - press enter key to end program");
        stop_program = user_input.nextLine();


    }
}

如何让while循环工作？

更新：在我获得了令人敬畏的反馈后，我终于得到了它的工作......感谢所有帮助过的人！

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        //declare all variables
        String sentence;
        int java_index_number;
        String stop_program;
        String java_capital_first_letter;
        String java_all_caps;

        //scanner to get user input
        Scanner user_input = new Scanner(System.in);

        //prompt the user for a sentence
        System.out.print("Enter a line of text containing the word 'java' somewhere within it: ");
        sentence = user_input.nextLine();


        while(!sentence.toLowerCase().contains("java")) {
            System.out.println("Your sentence does not have the word 'java' within it.");
            System.out.print("Enter a line of text containing the word 'java' somewhere within it: ");
            sentence = user_input.nextLine();
        }

        //output
        System.out.println();
        System.out.println("The string read is: " + sentence);
        System.out.println("Length in chars is: " + sentence.length());
        System.out.println("All lowercase is: " + sentence.toLowerCase());
        System.out.println("All uppercase is is: " + sentence.toUpperCase());

        //store java index pos in variable
        sentence = sentence.toLowerCase();
        java_index_number = sentence.indexOf("java");
        System.out.println("Found 'java' or at pos: " + java_index_number);


        //make first letter of java a capital letter
        java_capital_first_letter = sentence.substring(0, java_index_number) + sentence.substring(java_index_number,
                java_index_number + 1).toUpperCase() + sentence.substring(java_index_number + 1, java_index_number + 4)
                + sentence.substring(java_index_number + 4);

        //make java all caps
        java_all_caps = sentence.substring(0, java_index_number) + sentence.substring(java_index_number,
                java_index_number + 4).toUpperCase() + sentence.substring(java_index_number + 4);

        //output
        System.out.println("Changing to 'Java': " + java_capital_first_letter);
        System.out.println("Changing to 'JAVA': " + java_all_caps);

        // Keep console window alive until 'enter' pressed
        System.out.println();
        System.out.println("Done - press enter key to end program");
        stop_program = user_input.nextLine();


    }
}

Answer 1

问题在于你如何在while中创建boolean子句。所以，目前你有这个：

while(!sentence.contains(java) || !sentence.contains(Java) || !sentence.contains(JAVA))

假设句子包含＆＃34; java＆＃34;。所以，!sentence.contains(java)是假的。但是，!sentence.contains(Java)是正确的，因为句子包含＆＃34; java＆＃34;但不是＆＃34; Java＆＃34;。因为您正在使用逻辑OR（||），所以单个true足以使整个子句成立，并且执行while循环的内部。

你可能会这样做：

while(!sentence.contains(java) && !sentence.contains(Java) && !sentence.contains(JAVA))

在这种情况下，上面的所有条款都必须为真，这意味着句子不能包含＆＃34; java＆＃34;，＆＃34; Java＆＃34;或＆＃34; JAVA＆＃34;。

Answer 2

尽量避免使用＆＃34; Java＆＃34;的所有不同变量。我想你是在试图找到java出现的时候。所以适用于你的句子一个句子.toLowerCase（）。contains（＆＃34; java＆＃34;）用户输入将转换为小写，只检查是否包含小写的单词java，这样就可以避免使用这么多或者。在你的内部只需要一段时间（真实），并检查if（sentence.toLowerCase（）。contains（＆＃34; java＆＃34;））{break;}。

while loop：while句子不包含单词

2 个答案: