Working with Strings and StringBuffer/StringBuilder

In this section we'll discuss about String as well as its creation, polemic things like "Strings are immutable" and see wthat's going on behind the scenes also StringBuffer and StringBuilder will be on focus.

Let's take a look at how the string objects are created and understand the immutability.

	package br.com.ocjp.string;
	public class StringImmutable {
	public static void main(String[] args) {
	String st = new String("OCJP");
	String st2 = st;
	st = st.concat(" - Java");
	System.out.println("st variable ==> " + st);
	System.out.println("st2 variable ==> " + st2);
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

	package br.com.ocjp.string;
	public class StringImmutable {
	public static void main(String[] args) {
	String book = new String("Book");
	book.concat(" - Java");
	book.upperCase();
	System.out.println("book variable ==> " + book); // it prints "Book"
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

As you can see it prints "Book" because we don't refer the new String created to "Java - Book", so the object is in the heap however nobody refers to it.

Commom methods
Let's see common methods in action.

	package br.com.ocjp.string;
	public class StringCommon {
	public static void main(String[] args) {
	String example = "Java Example ";
	System.out.println("charAt() ==> " + example.charAt(0)); // it prints J
	System.out.println("concat() ==> " + example.concat(" -1")); // it prints Java Example - 1
	System.out.println("equalsIgnoreCase() ==> " + example.equalsIgnoreCase("java example ")); // it prints true
	System.out.println("length() ==> " + example.length()); // it prints 14
	System.out.println("replace() ==> " + example.replace("a","@")); // it prints J@v@ Ex@mple
	System.out.println("substring() ==> " + example.substring(0)); // it prints Java Example
	System.out.println("substring() ==> " + example.substring(0,4)); // it prints Java
	System.out.println("toLowerCase() ==> " + example.toLowerCase()); // it prints java example
	System.out.println("toString() ==> " + example.toString()); // it prints Java Example
	System.out.println("toUpperCase() ==> " + example.toUpperCase()); // it prints JAVA EXAMPLE
	System.out.println("trim() ==> " + example.trim()); // no space at the end... it prints Java Example
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

Pool of String

	package br.com.ocjp.string;
	public class StringPool {
	public static void main(String[] args) {
	String t = "java"; // Creates an object in a heap and puts it in a pool of String
	String t1 = new String("java"); //Creates a new object in a heap and puts it in a pool of String
	System.out.println(t == t1); // prints false
	String s = "ocjp";
	String s1 = "ocjp"; // Retrieve the string ocjp from the pool
	System.out.println(s == s1); // prints true
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

Also you can use the method intern() (String class) this way we can get the string from the pool if the string pass using the method equals().


StringBuffer and StringBuilder friends of memory

Both classes are intented to help you handle Strings without wasting memory, as we mentioned Strings are immutable and if we have to handle lots and lots of them StringBuffer and StringBuilder will help you.
The unique difference between StringBuffer and StringBuilder is StringBuilder is not thread-safe which means its methods aren't synchronized, as you can imagine StringBuilder is faster than StringBuffer.

	package br.com.ocjp.string;
	public class StringBufferBuilder {
	public static void main(String[] args) {
	StringBuffer sb = new StringBuffer();
	sb.append("Java Test - ");
	sb.append("OCJP");
	System.out.println(sb); // Prints Java Test - OCJP
	StringBuffer sd = new StringBuffer("0123456789");
	sd.delete(4, 6);
	System.out.println(sd); //Prints 01236789
	StringBuffer si = new StringBuffer("0123456789");
	si.insert(4, "----");
	System.out.println(si); //Prints 0123----46789
	StringBuffer sr = new StringBuffer("0123456789");
	sr.reverse();
	System.out.println(sr); //Prints 987654321
	StringBuilder builder = new StringBuilder("abcdef");
	builder.append("ghij").reverse().delete(5,20);
	System.out.println(builder); // Prints jihgf
	}
	}

view raw gistfile1.java hosted with ❤ by GitHub

The most import thing here is StringBuffer and StringBuilder are not immutable like String and the StringBuffer contains the synchronized methods;