Java String Class Example--reference

"Hello World"?is called a?String?literal. In a Java program,everything between two double quotes is a?String?literal. Literals are implemented as instances of String class. As you can see,you can conveniently initialize a?String?Object like a primitive type,e.g?int i = 0;.

There is no need to do:

There is a difference between these two initialization methods,although the result is the same : A?String?with value “Hello World”. But more on that in just a bit.

For now,here is a simple?main?with the most important?String?API methods:

StringClassExample.java

This is the output of the above program:

str1:Hello World
str2:Hello
str3:Hello World
11
Length: 7
Substring :llo Worl
Literal Substring :bcd
Char array : [l,l,o]
Index of 'W':6
Index of 'orld':7
LAST Index of 'l':9
LAST Index of 'l':3
Character at position 5: 
abcefafa
ABCASIPASC
Hell0 W0rld
    Java
Java
Java,is,great
Java,great,J,a,v,i,s,Contains :true
Equals :false
Equals ignore case:true
Compare:-23
false
true

From the above program is clear that Java designers decided to treat Strings somewhat differently from other Objects. For example you can initialize them like a primitive,e.g?String a="abc"?and you can concatenate two strings using?+?operator,like you would add twoints?(looks like overloading + operator in C++).

The?comparison attempts?section of the code might seem a little fuzzy,but it will get clear in the next section. What you should take away from it now,is that you SHOULD NEVER try to compare the contents of Strings using?==?operator. You are only comparing reference equality,not content equality. You MUST use?equals?or?equalsIgnoreCase.

3. Other characteristics of String objects

String?objects are immutable. This means that once a?String?is created,its contents cannot be changed. In the above example,every time we attempt to change its contents,e.g when concatenating,a new?String?object is created representing the result. Additionally,String class is final,so you cannot override its behavior.

Immutability was mostly chosen for security reasons and for performance. It also means that two different thread can share the same String and manipulate it as they want,not having to synchronize anything,because every time they make a change in the original string,a new one is created,while the old one remains untouched.

Now let’s see this :

true
false

true
false
true