java - while 循环 : while sentence does not contain a word

Question

我正在获取用户输入并检查句子中是否包含“java”一词。我做了一个 while 循环，但即使句子中有“java”这个词，它也告诉我它不是，并继续 while 循环。如果我删除 while 循环，我希望我的程序执行的所有其他操作都有效。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:在收到很棒的反馈后，我终于开始工作了。感谢所有提供帮助的人!

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

问题在于您如何在 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))

假设句子中包含“java”。所以，!sentence.contains(java) 是错误的。但是，!sentence.contains(Java) 是正确的，因为该句子包含“java”但不包含“Java”。因为您使用的是逻辑 OR (||)，所以单个 true 足以使整个子句为 true，并执行 while 循环的内部。

您尝试做的事情可能会以这种方式完成:

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

在这种情况下，上述所有子句都必须为真，这意味着该句子不能包含“java”、“Java”或“JAVA”。