How can you represent the subtraction of two strings in Java?

In Java, strings are immutable, which means you cannot directly subtract two strings using the subtraction operator. However, you can achieve the effect of subtracting strings by using methods from the String class.

One common method is to use the replace method from the String class to delete the second string from the first string. For example:

String str1 = "Hello World";
String str2 = "World";
String result = str1.replace(str2, "");
System.out.println(result); // 输出：Hello 

In the above code, two strings, str1 and str2, are first defined. The replace method is then used to delete str2 from str1 and save the result in the variable result. Finally, by printing result, the result of subtracting the strings can be obtained.

Another method is to use regular expressions, by treating the second string as part of the regular expression, and replacing it with an empty string. For example:

String str1 = "Hello World";
String str2 = "World";
String result = str1.replaceAll(str2, "");
System.out.println(result); // 输出：Hello 

In the above code, the replaceAll method is used to treat str2 as a regular expression and replace it with an empty string to get the result of subtracting the strings.

It is important to note that both methods create a new string as the result and do not modify the original string object. If you need to modify the original string object, you can reassign the result to the original string variable.