String类中的常用方法

爱被打了一巴掌 2023-10-01 22:28 7阅读 0赞

## 方法 ##

<table> 
 <thead> 
  <tr> 
   <th><code>charAt(int index)</code></th> 
   <th>返回 <code>char</code>指定索引处的值。</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><code>codePointAt(int index)</code></td> 
   <td>返回指定索引处的字符（Unicode代码点）</td> 
  </tr> 
  <tr> 
   <td><code>codePointBefore(int index)</code></td> 
   <td>返回指定索引之前的字符（Unicode代码点）。</td> 
  </tr> 
  <tr> 
   <td><code>concat(String str)</code></td> 
   <td>将指定的字符串连接到该字符串的末尾。</td> 
  </tr> 
  <tr> 
   <td><code>contains(CharSequence s)</code></td> 
   <td>当且仅当此字符串包含指定的char值序列时才返回true。</td> 
  </tr> 
  <tr> 
   <td><code>endsWith(String suffix)</code></td> 
   <td>测试此字符串是否以指定的后缀结尾。</td> 
  </tr> 
  <tr> 
   <td><code>equals(Object anObject)</code></td> 
   <td>将此字符串与指定对象进行比较。</td> 
  </tr> 
  <tr> 
   <td><code>hashCode()</code></td> 
   <td>返回此字符串的哈希码</td> 
  </tr> 
  <tr> 
   <td><code>indexOf(String str, int fromIndex)</code></td> 
   <td>返回指定子串的第一次出现的字符串内的索引，以指定的索引开始搜索。 formIndex可以不传</td> 
  </tr> 
  <tr> 
   <td><code>isEmpty()</code></td> 
   <td>返回 <code>true</code>如果，且仅当 <a rel="nofollow"><code>length()</code></a>为 <code>0</code> 。</td> 
  </tr> 
  <tr> 
   <td><code>lastIndexOf(String str, int fromIndex)</code></td> 
   <td>返回指定子字符串的最后一次出现的字符串中的索引，从指定索引开始向后搜索。 formIndex可以不传</td> 
  </tr> 
  <tr> 
   <td><code>length()</code></td> 
   <td>返回此字符串的长度</td> 
  </tr> 
  <tr> 
   <td><code>replace(char oldChar, char newChar)</code></td> 
   <td>返回从替换所有出现的导致一个字符串 <code>oldChar</code>在此字符串 <code>newChar</code></td> 
  </tr> 
  <tr> 
   <td><code>replace(CharSequence target, CharSequence replacement)</code></td> 
   <td>将与字面目标序列匹配的字符串的每个子字符串替换为指定的字面替换序列。</td> 
  </tr> 
  <tr> 
   <td><code>split(String regex)</code></td> 
   <td>将此字符串分割为给定的 <a rel="nofollow">regular expression的</a>匹配。</td> 
  </tr> 
  <tr> 
   <td><code>startsWith(String prefix)</code></td> 
   <td>测试此字符串是否以指定的前缀开头。</td> 
  </tr> 
  <tr> 
   <td><code>substring(int beginIndex, int endIndex)</code></td> 
   <td>返回一个字符串，该字符串是此字符串的子字符串。 endIndex可以不传</td> 
  </tr> 
  <tr> 
   <td><code>toCharArray()</code></td> 
   <td>将此字符串转换为新的字符数组。</td> 
  </tr> 
  <tr> 
   <td><code>toLowerCase()</code></td> 
   <td>将所有在此字符 <code>String</code>使用默认语言环境的规则，以小写。</td> 
  </tr> 
  <tr> 
   <td><code>toUpperCase()</code></td> 
   <td>将所有在此字符 <code>String</code>使用默认语言环境的规则大写。</td> 
  </tr> 
 </tbody> 
</table>

## 使用样例 ##

public class StringTest {
        private static String str = "1,a,2,b,3,c";
    
        public static void main(String[] args) {
            System.out.println("charAt: "+ str.charAt(0));
            System.out.println("codePointAt: " + str.codePointAt(0));
            System.out.println("codePointBefore: " + str.codePointBefore(3));
            System.out.println("concat: " + str.concat(","));
            System.out.println("contains: " + str.contains(","));
            System.out.println("endsWith: " + str.endsWith(","));
            System.out.println("equals: " + str.equals("ss"));
            System.out.println("hashCode: " + str.hashCode());
            System.out.println("indexOf: " + str.indexOf(",", 2));
            System.out.println("isEmpty: " + str.isEmpty());
            System.out.println("lastIndexOf: " + str.lastIndexOf(","));
            System.out.println("length: " + str.length());
            System.out.println("replace1: " + str.replace("a", "A"));
            System.out.println("replace2: " + str.replace("a,2,b", "A,2,B"));
            String[] split = str.split(",");
            for (String s : split) {
                System.out.print(s);
            }
            System.out.println();
            System.out.println("startsWith: " + str.startsWith("1"));
            System.out.println("substring: " + str.substring(3, 5));
            char[] chars = str.toCharArray();
            for (char aChar : chars) {
                System.out.print(aChar);
            }
            System.out.println();
            System.out.println("toUpperCase: " + str.toUpperCase());
            System.out.println("toLowerCase: " + str.toUpperCase().toLowerCase());
        }
    }

### 控制台打印 ###

charAt: 1
    codePointAt: 49
    codePointBefore: 97
    concat: 1,a,2,b,3,c,
    contains: true
    endsWith: false
    equals: false
    hashCode: 713949408
    indexOf: 3
    isEmpty: false
    lastIndexOf: 9
    length: 11
    replace1: 1,A,2,b,3,c
    replace2: 1,A,2,B,3,c
    1a2b3c
    startsWith: true
    substring: ,2
    1,a,2,b,3,c
    toUpperCase: 1,A,2,B,3,C
    toLowerCase: 1,a,2,b,3,c