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String (Literal & Class)

3 min read

Overview

Represents a combination of characters that make up a string

  • String is a class so when we make a new string we’re actually creating an object
  • You can create String objects using string literals or the new keyword
  • String is immutable! → Use StringBuffer (or the more modern StringBuilder) when you need a mutable string
  • You MUST use " and not ', since ' is reserved for chars

Basics

// same thing
String myString = new String("aBc"); // new keyword 
String myString = "aBc"; // String literal
 
// returns new string
System.out.println(myString.toUpperCase()) // ABC
System.out.println(myString.toLowerCase()) // abc
System.out.println(myString)               // aBc
 
// string concatenation
System.out.println(a + "+" + b " = " + (a + b));
System.out.println("데카르트는 \"나는 생각한다. 고로 존재한다.\"라고 말했다.");
  • String myString = new String("aBc");
    • myString reference is stored in the stack, and the String object itself is stored in the heap
    • Java’s Memory Model
  • string concatenation
    • Combining several strings into a single string, or combining a string with other data into a new, longer string.
    • often used to report the value of a variable
  • print VS println
    • println: sends output to current line then moves to the beginning of a new line
    • print: only sends output to current line
      • so it doesn’t go to the beginning of a new line

String Literal

String s1 = "hello";
String s2 = "hello";
  • s1 and s2 are references pointing to String objects.
  • All string literals in a special area of memory called the String Constant Pool.
  • How it works: When you create s1, Java puts the object "hello" into the pool. When you create s2, Java checks the pool, sees that "hello" already exists, and simply makes s2 point to that exact same object.
    • They point to the same place in memory!

String class: new keyword

String s3 = new String("hello");
String s4 = new String("hello");
  • Explicitly creates a new object every time!
  • The new keyword forces Java to create a brand new String object in the main memory area (the heap), completely separate from the String Constant Pool.
  • How it works: Even though s3 and s4 contain the exact same characters, they are two distinct objects in different memory locations.

Escape sequences

  • two-character sequences used to represent special characters, all beginning with \
System.out.println("What \"characters\" does this \\ print?");
// Output: What "characters" does this \ print?
  • Use \n for line break

StringBuffer

StringBuffer s = new StringBuffer("hello");
s.append("!"); //s = "hello!"

Comparison

// comparing
String myString = "aBc";
System.out.println(myString.toLowerCase() == "abc"); // comparing instances (addresses)
System.out.println(myString.toLowerCase().equals("abc")); // comparing values
  • If you compare 2 primitives types, you compare the value
  • If you compare 2 reference types, you compare if they point to the same instances

Graph View

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