I. Illustration: the String in Java is non-mutable. javastring

I. Illustration: the String in Java is non-mutable. javastring

Here are a bunch of examples to illustrate the immutable Java String.

1. Declare a String

String s = "abcd";

The s Variable saves the reference of the string object. The arrows below explain the reference of the object that is saved.

 

2. assign a value to a String variable to another String variable.

String s2 = s;

The String object is unchangeable. The 2 variable s2 stores the same referenced values, all of which point to the same object value.

 

3. Connect to String

 

s = s.concat("ef");

The variable s now stores references to the newly created sting object.

 

Summary:
Once a string is created in the memory (HEAP), it cannot be changed. We should note that all the String methods will not change a string, but return a new string.

If we need a string that can be changed, we can use StringBuffer or StringBuilder. Otherwise, a large amount of time is wasted on garbage collection every time a new string is created.

Here is an application example of StringBuilder.

public static String readFileToString() throws IOException {        File dirs = new File(".");        String filePath = dirs.getCanonicalPath() + File.separator+"src"+File.separator+"TestRead.java";         StringBuilder fileData = new StringBuilder(1000);//Constructs a string buffer with no characters in it and the specified initial capacity        BufferedReader reader = new BufferedReader(new FileReader(filePath));         char[] buf = new char[1024];        int numRead = 0;        while ((numRead = reader.read(buf)) != -1) {            String readData = String.valueOf(buf, 0, numRead);            fileData.append(readData);            buf = new char[1024];        }         reader.close();         String returnStr = fileData.toString();        System.out.println(returnStr);        return returnStr;    }