使用Java编写的菜单驱动程序，用于执行基本的字符串操作
String指的是一系列的字符。在Java中，String是对象。为了创建和操作字符串，Java提供了String类。String类有许多内置方法，用于不同的目的。
We will perform a few basic string operations by using inbuilt String methods.
replace() Method: It replaces a specified character in the given string. concat() Method: It appends another string to the end of one string. length() Method: It returns the length of the given String. Equals() Method: It checks whether two strings are equal or not.
在本文中，我们将学习一些基本的字符串操作，如连接两个字符串、计算字符串长度、使用Java编程语言比较两个字符串。我们将使用switch case来实现应用程序。
展示一些实例给你看−
Instance-1
的中文翻译为：
实例-1
Suppose the first String is ‘Java’ and the second String is ‘Python’ then by joining two String will give ‘JavaPython’. Here the concat() method will be used.
Instance-2
Suppose the first String is ‘Java’ and the second String is ‘Python’ then by counting two String will give its respective length as 4 and 6. Here length() method will be used.
Instance-3
Suppose the first String is ‘Java’ and the second String is ‘Python’ then by comparing two String will give “Both strings are not equal”. Here equals() method will be used.
Instance-4
翻译成中文为：
实例-4
假设字符串为‘Java’，将字母‘J’替换为‘R’，那么新的字符串将是Rava。在这里将使用replace()方法。
语法
To perform basic string operations like joining the string, getting length of the string, comparing the string and replacing a specific value in a String we use concat(), length(), equals() and replace() methods respectively. The concat() method appends (concatenate) a string to the end of another string. The length() method returns the length of a specified string. The length of an empty string is 0. The equals() method compares two strings, and returns true if the strings are equal, and false if not. The replace() method replaces a specified value in a String with another new value.
以下是“for循环”的语法 -
for (statement 1; statement 2; statement 3) {
// code block to be executed
}
Following is the syntax for concat function
string1.concat(string2)
以下是length函数的语法
string1.length()
Following is the syntax for equals function
string1.equals(string2)
以下是replace函数的语法
string1.replace(‘OldValue’, ‘NewValue’)
算法
Step-1 − Declare a String variable and initialize the value.
第二步 - 显示菜单。
Step-3 − Ask the user to enter their choice.
Step-4 − Use a switch case to go to the choice and perform the operation.
步骤-5 − 打印结果。
让我们看一下程序，以便更清楚地理解它。
Example
的中文翻译为：
示例
<span class="token keyword">import</span> <span class="token namespace">java<span class="token punctuation">.</span>util<span class="token punctuation">.</span></span><span class="token operator">*</span><span class="token punctuation">;</span>
<span class="token keyword">public</span> <span class="token keyword">class</span> <span class="token class-name">Main</span><span class="token punctuation">{</span>
<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span> args<span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"First String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> s1 <span class="token operator">=</span> <span class="token string">"Hello"</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Second String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">String</span> s2 <span class="token operator">=</span> <span class="token string">"World"</span><span class="token punctuation">;</span>
mainLoop<span class="token operator">:</span> <span class="token keyword">while</span> <span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">Scanner</span> inn <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">Scanner</span><span class="token punctuation">(</span> <span class="token class-name">System</span><span class="token punctuation">.</span>in <span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"\n***Menu***"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"1. Join Two Strings"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"2. Get length of a String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"3. Compare two Strings"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"4. Replace a value in String"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"5. Terminate the program"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Enter action number (1-5): "</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> command<span class="token punctuation">;</span>
<span class="token keyword">if</span> <span class="token punctuation">(</span>inn<span class="token punctuation">.</span><span class="token function">hasNextInt</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">{</span>
command <span class="token operator">=</span> inn<span class="token punctuation">.</span><span class="token function">nextInt</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
inn<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">else</span><span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"\nILLEGAL RESPONSE. YOU MUST ENTER A NUMBER."</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
inn<span class="token punctuation">.</span><span class="token function">nextLine</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">continue</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">switch</span><span class="token punctuation">(</span>command<span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token keyword">case</span> <span class="token number">1</span><span class="token operator">:</span>
<span class="token class-name">String</span> joinedString <span class="token operator">=</span> s1<span class="token punctuation">.</span><span class="token function">concat</span><span class="token punctuation">(</span>s2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Joined String: "</span> <span class="token operator">+</span> joinedString<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">break</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token number">2</span><span class="token operator">:</span>
<span class="token keyword">int</span> length1 <span class="token operator">=</span> s1<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Length of first String: "</span> <span class="token operator">+</span> length1<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">int</span> length2 <span class="token operator">=</span> s2<span class="token punctuation">.</span><span class="token function">length</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Length of second String: "</span> <span class="token operator">+</span> length2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">break</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token number">3</span><span class="token operator">:</span>
<span class="token keyword">boolean</span> result <span class="token operator">=</span> s1<span class="token punctuation">.</span><span class="token function">equals</span><span class="token punctuation">(</span>s2<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">if</span><span class="token punctuation">(</span>result <span class="token operator">==</span> <span class="token boolean">true</span><span class="token punctuation">)</span> <span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Strings first and second are equal"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">else</span><span class="token punctuation">{</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Strings first and second are not equal"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token keyword">break</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token number">4</span><span class="token operator">:</span>
<span class="token class-name">String</span> newString <span class="token operator">=</span> s2<span class="token punctuation">.</span><span class="token function">replace</span><span class="token punctuation">(</span><span class="token string">'W'</span><span class="token punctuation">,</span> <span class="token string">'Z'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"After replacing the new string is: "</span><span class="token operator">+</span>newString<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">break</span><span class="token punctuation">;</span>
<span class="token keyword">case</span> <span class="token number">5</span><span class="token operator">:</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Program terminated"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">break</span> mainLoop<span class="token punctuation">;</span>
<span class="token keyword">default</span><span class="token operator">:</span>
<span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Wrong choice!!"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
<span class="token punctuation">}</span>
输出
First String Second String ***Menu*** 1. Join Two Strings 2. Get length of a String 3. Compare two Strings 4. Replace a value in String 5. Terminate the program Enter action number (1-5): 2 Length of first String: 5 Length of second String: 5 ***Menu*** 1. Join Two Strings 2. Get length of a String 3. Compare two Strings 4. Replace a value in String 5. Terminate the program Enter action number (1-5): 1 Joined String: HelloWorld ***Menu*** 1. Join Two Strings 2. Get length of a String 3. Compare two Strings 4. Replace a value in String 5. Terminate the program Enter action number (1-5): 4 After replacing the new string is: Zorld ***Menu*** 1. Join Two Strings 2. Get length of a String 3. Compare two Strings 4. Replace a value in String 5. Terminate the program Enter action number (1-5): 3 Strings first and second are not equal ***Menu*** 1. Join Two Strings 2. Get length of a String 3. Compare two Strings 4. Replace a value in String 5. Terminate the program Enter action number (1-5): 5 Program terminated
在本文中，我们通过使用菜单驱动的方法，探讨了如何在Java中执行简单的字符串操作。
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