Strings

String is collection of characters.

String syntax:

String str = "Hello";
// or
String str = new String("Hello");

String Concatenation

String fName = "Foo";
String lName = "Bar";

String name = fName + " " + lName;

When using concatenation operator with strings, we should be careful.

int x = 10, y = 20;
System.out.println(x + y + " is Sum");          // 30 is Sum

int x = 10, y = 20;
System.out.println("Sum is " + x + y);          // Sum is 1020

This happened because of precedence...

Firstly, It became ("Sum is " + x) = Sum is 10

Then, It became ("Sum is 10" + y) = Sum is 1020

So, we can use braces to set the precedence.

int x = 10, y = 20;
System.out.println("Sum is " + (x + y));          // Sum is 30

Accessing String Characters

String str = "Foo Bar";

System.out.println(str.charAt(1));              // o

We can access each character using this method.

String Comparison

String s1 = "Foo";
String s2 = "Foo";
String s3 = new String("Foo");

System.out.println( s1 == s2 );             // true

System.out.println( s1 == s3 );             // false
System.out.println( s1.equals(s3) );        // true

This happened because, when we created string variable s2 without new keyword, String s2 also started pointing to the same string to which s1 is pointing.

It is also called Interning.

But, using equals() function, the actual value of the string was compared, instead of its pointer.

String Lexicographic Comparison

str1.compareTo(str2);

If value is 0, means strings are equal.

If value is less than 0, means str1 is less than str2

If value is greater than 0, means str1 is greater than str2

For example,
- Java is greater than Cpp, because (74 > 67) i.e. (J > C)
- ABC is smaller than abc, because (65 < 97) i.e. (A < a)

String Builder

When we modify existing string, a new string is created inside the memory.

For example,

String str = new String("Hello");

str = str + 'A';

Now, a new string is created HelloA, and str will point to the new string.

This is because, Strings are immutable in java.

String Builder is a mutable string class.

StringBuilder sb = new StringBuilder("Hello");

toString() functions converts a object into string.

For example,

int a = 10;
a.toString();               // Incorrect, since a is not object

char ch = 'a';
ch.toString();              // Incorrect, since ch is not object

Integer a = 10;
a.toString();               // Correct

Character ch = 'a';
ch.toString();              // Correct

Adding Characters

We can add characters in the StringBuilder object, by using append() method.

It appends character to the end of the string.

StringBuilder sb = new StringBuilder("");
sb.append("Hello");
System.out.println(sb);

Last modified: 08 February 2026