编写一个Java程序，将句子中每个单词的首字母大写

Question

Write a Java program to capitalize the first letter of each word in a sentence.

为此，我编写了一个 java 程序，但它抛出了一个错误

"result of string.replace(),is ignored";

我的代码

package com.company;

import java.util.Scanner;

public class uppercase_1srchar_of_string {
    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);
        System.out.println("enter the string :");
        String a = sc.nextLine();

        for(int i = 0; i < a.length(); i++) {
            if(a.charAt(i) == ' ') {
                char c;
                char d;
                c = a.charAt((i + 1));
                d = Character.toUpperCase(c);
                a.replace(a.charAt((i + 1)),d);
            }
        }

        System.out.println(a);
    }
}

不知道哪里弄错了

Answer 1

Java 的 String.replace 方法不会对字符串进行突变，它 returns 一个执行了替换的新字符串。

参见 here。

您需要重新考虑您的设计。一种方法是复制字符串，然后扫描原始字符串，同时逐步替换副本。

像这样：

package com.company;

import java.util.Scanner;

public class uppercase_1srchar_of_string {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("enter the string :");
        String a = sc.nextLine();

        String b = a;
        for (int i = 0; i < a.length(); i++) {
            if (a.charAt(i) == ' ') {
                char c = a.charAt((i + 1));
                char d = Character.toUpperCase(c);
                
                b = b.replace(a.charAt(i + 1), d);
            }
        }

        System.out.println(a);
    }
}

您甚至可以像这样替换 a：

package com.company;

import java.util.Scanner;

public class uppercase_1srchar_of_string {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        System.out.println("enter the string :");
        String a = sc.nextLine();

        for (int i = 0; i < a.length(); i++) {
            if (a.charAt(i) == ' ') {
                char c = a.charAt((i + 1));
                char d = Character.toUpperCase(c);

                a = a.replace(a.charAt(i + 1), d);
            }
        }

        System.out.println(a);
    }
}

Answer 2

使用replaceAll

String a = "Write a Java program to capitalize the first letter of each word in a sentence.";

String b = Pattern
        .compile("([^a-zA-Z]*)([a-zA-Z]+)")
        .matcher(a)
        .replaceAll(w ->
                w.group(1) + w.group(2).substring(0, 1).toUpperCase() + w.group(2).substring(1));

System.out.println(b);

有输出

Write A Java Program To Capitalize The First Letter Of Each Word In A Sentence.

（注：词义定义不明确，根据需要改见例https://www.jrebel.com/blog/java-regular-expressions-cheat-sheet）

Answer 3

这里是 Java 的流畅代码，可以在完全不使用替换方法的情况下执行相同的操作，

import java.util.Arrays;
import java.util.stream.Collectors;

public class HelloWorld{

     public static void main(String []args){
        String data = "Hello world is my 1st program, wow i am amazed";
        String output = Arrays.stream(data.split(" "))
                              .map(word -> Character.toUpperCase(word.charAt(0)) + word.substring(1))
                              .collect(Collectors.joining(" "));
                              
        System.out.println("Output: " + output);
     }
}

输出如下，

Output: Hello World Is My 1st Program, Wow I Am Amazed

您可以在 https://www.tutorialspoint.com/compile_java8_online.php

在线尝试上述解决方案

编写一个Java程序，将句子中每个单词的首字母大写

Write a Java program to capitalize the first letter of each word in a sentence

java

str-replace