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                # Java `String contains()`方法 > 原文: [https://beginnersbook.com/2017/10/java-string-contains-method/](https://beginnersbook.com/2017/10/java-string-contains-method/) Java `String contains()`方法檢查特定字符序列是否是給定字符串的一部分。如果給定字符串中存在指定的字符序列,則此方法返回`true`,否則返回`false`。 **例如:** ```java String str = "Game of Thrones"; //This will print "true" because "Game" is present in the given String System.out.println(str.contains("Game")); /* This will print "false" because "aGme" is not present, the characters * must be present in the same sequence as specified in the contains method */ System.out.println(str.contains("aGme")); ``` ## `contains()`方法的語法 ```java public boolean contains(CharSequence str) ``` 返回類型是`boolean`,這意味著此方法返回`true`或`false`。當在給定字符串中找到字符序列時,此方法返回`true`,否則返回`false`。 如果`CharSequence`為`null`,則此方法拋出`NullPointerException`。 例如:像這樣調用此方法會拋出`NullPointerException`。 ```java str.contains(null); ``` ## Java `String contains()`方法示例 第二個`print`語句顯示為`false`,因為`contains()`方法區分大小寫。 **您也可以使用`contains()`方法進行不區分大小寫的檢查**,我已經在本教程末尾介紹了。 ```java class Example{ public static void main(String args[]){ String str = "Do you like watching Game of Thrones"; System.out.println(str.contains("like")); /* this will print false as the contains() method is * case sensitive. Here we have mentioned letter "l" * in upper case and in the actual string we have this * letter in the lower case. */ System.out.println(str.contains("Like")); System.out.println(str.contains("Game")); System.out.println(str.contains("Game of")); } } ``` **輸出:** ```java true false true true ``` ## 示例 2:在`if-else`語句中使用 Java `String contains()`方法 我們知道`contains()`方法返回一個布爾值,我們可以將此方法用作[`if-else`語句](https://beginnersbook.com/2017/08/if-else-statement-in-java/)中的條件。 ```java class JavaExample{ public static void main(String args[]){ String str = "This is an example of contains()"; /* Using the contains() method in the if-else statement, since * this method returns the boolean value, it can be used * as a condition in if-else */ if(str.contains("example")){ System.out.println("The word example is found in given string"); } else{ System.out.println("The word example is not found in the string"); } } } ``` **輸出:** ![Java String contains method example](https://img.kancloud.cn/3f/7e/3f7e0387cad3884a9752ac997b8e0b61_1024x659.jpg) ## Java `String contains()`方法,用于不區分大小寫的檢查 我們在上面已經看到`contains()`方法區分大小寫,但是通過一個小技巧,您可以使用此方法進行不區分大小寫的檢查。讓我們舉個例子來理解這個: 這里我們使用[`toLowerCase()`方法](https://beginnersbook.com/2013/12/java-string-tolowercase-method-example/)將兩個字符串轉換為小寫,以便我們可以使用`contains()`方法執行不區分大小寫的檢查。我們也可以使用`toUpperCase()`方法實現同樣的目的,如下例所示。 ```java class Example{ public static void main(String args[]){ String str = "Just a Simple STRING"; String str2 = "string"; //Converting both the strings to lower case for case insensitive checking System.out.println(str.toLowerCase().contains(str2.toLowerCase())); //You can also use the upper case method for the same purpose. System.out.println(str.toUpperCase().contains(str2.toUpperCase())); } } ``` 輸出: ```java true true ``` #### 參考: [`String Contains()`方法 JavaDoc](https://docs.oracle.com/javase/7/docs/api/java/lang/String.html#contains(java.lang.CharSequence))
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