转义字符'\\'不在System.out.println（）中显示，但在返回值中显示

Question

In Java, when I replace characters in a String with escaped-characters, the characters show up in the return value, although they were not there according to System.out.println .

String[][][] proCategorization(String[] pros, String[][] preferences) {
String str = "wehnquflkwe,wefwefw,wefwefw,wefwef"; 
String strReplaced = str.replace(",","\",\""); //replace , with ","
System.out.println(strReplaced);

The console output is: wehnquflkwe","wefwefw","wefwefw","wefwef

String[][][] array3d = new String[1][1][1]; // initialize 3d array
array3d[0][0][0] = strReplaced;
System.out.println(array3d[0][0][0]);


    return array3d;
}

The console output is:

wehnquflkwe","wefwefw","wefwefw","wefwef

Now the return value is:

[[["wehnquflkwe\\",\\"wefwefw\\",\\"wefwefw\\",\\"wefwef"]]]

I don't understand why the \\ show up in the return value but not in the System.out.println .

Answer 1

Characters in memory can be represented in different ways.

Your integrated development environment (IDE) has a debugger that chooses to represent a String[][][] with a single element that contains the characters

wehnquflkwe","wefwefw","wefwefw","wefwef

as a java-quoted string

"wehnquflkwe\",\"wefwefw\",\"wefwefw\",\"wefwef" 

this makes a lot of sense, because you can then copy and paste this string into java code without any loss.

On the other hand, your system's console, and the IDE's built-in terminal emulator, will output the characters in their normal representation, that is, without any java string-escape-characters:

wehnquflkwe","wefwefw","wefwefw","wefwef

As an experiment, you may want to check what happens with other "special" characters, such as \\t (a tab break) or \\b (backspace). This is just the tip of the iceberg - characters in Java generally translate into unicode points, which may or may not be supported by the fonts available in your system or terminal. The IDE's way of representing characters as java-quoted strings allows it to losslessly represent pretty much anything; System.out.println's output is a lot more variable.

Answer 2

System.out.println prints the String exactly as it is stored in memory.

On the other hand, when you stop the application flow using a breakpoint you are able to look up the values.

Most of the IDEs display escape characters with \\ to indicate that it's just one String , not String[] in this case, or not to split the String into two lines if it contains \\n in the middle.

Just in case, you still have doubts, I suggest printing strReplaced.length() . This should allow you to count characters one by one.

Possible experiments:

String s = "my cute \n two line String";
System.out.println(s + " length is: " + s.length());