Strings

We have briefly mentioned the concept of a String in Java. A String is a sequence of characters, which we denote surrounded by double-quotes (e.g., "Hello World!").

String Concatenation

You can make variables of type String and you can even use + to combine Strings together with string concatenation.

JAVA

String greeting = "Hello";
String location = "Seattle";
String result = greeting + " " + location + "!";
System.out.println(result);

// Output:
// Hello Seattle!

PYTHON

greeting = "Hello"
location = "Seattle"
result = greeting + " " + location + "!"
print(result)

# Output:
# Hello Seattle!

JAVASCRIPT

let greeting = "Hello";
let location = "Seattle";
let result = greeting + " " + location + "!";
console.log(result);

// Output:
// Hello Seattle!

C

#include <stdio.h>
#include <string.h>

char result[50]; // buffer to hold result
char *greeting = "Hello";
char *location = "Seattle";
strcpy(result, greeting);
strcat(result, " ");
strcat(result, location);
strcat(result, "!");
printf("%s\n", result);

// Output:
// Hello Seattle!

C++

#include <iostream>

using namespace std;

string greeting = "Hello";
string location = "Seattle";
string result = greeting + " " + location + "!";
cout << result << endl;

// Output:
// Hello Seattle!

In Java, you can also concatenate Strings with other data types, and they will be converted to Strings!

JAVA

String s1 = "a";
String s2 = s1 + 4;
System.out.println(s2);  // a4

PYTHON

s1 = "a"
s2 = s1 + str(4)
print(s2)  # a4

JAVASCRIPT

let s1 = "a";
let s2 = s1 + 4;
console.log(s2); // a4

C

char *s1 = "a";
char s2[2];
strcpy(s2, s1);
strcat(s2, "4");
printf("%s\n", s2); // a4

C++

string s1 = "a";
string s2 = s1 + "4";
cout << s2 << endl; // a4

String Methods

Earlier, we mentioned that String is a bit special compared to other data types, indicated by having an upper-case name compared to the primitive data types such as int. This is because String is an example of a special “object type” that carries more complex functionalities. For example, you can ask Strings to perform more complicated operation by calling methods on them. The following code snippet shows many of the most common methods useful for Strings. You can learn about more of the methods here.

JAVA

String s1 = "Hello";

String s2 = s1.toUpperCase();  // "HELLO"
String s3 = s1.toLowerCase();  // "hello"

String s4 = s1.substring(1, 4);  // "ell"
String s5 = s1.substring(2);     // "llo"

char c = s1.charAt(1);    // 'e'
int i = s1.indexOf('l');  // 2

PYTHON

s1 = "Hello"

s2 = s1.upper()  # "HELLO"
s3 = s1.lower()  # "hello"

s4 = s1[1:4]  # "ell"
s5 = s1[2:]   # "llo"

c = s1[1]          # "e"
i = s1.index("l")  # 2

JAVASCRIPT

let s1 = "Hello";

let s2 = s1.toUpperCase();  // "HELLO"
let s3 = s1.toLowerCase();  // "hello"

let s4 = s1.substring(1, 4);  // "ell"
let s5 = s1.substring(2);     //"llo"

let c = s1[1];            // "e"
let i = s1.indexOf("l");  // 2

C

#include <stdio.h>
#include <string.h>
#include <ctype.h>

char *s1 = "Hello";
unsigned long int s1_len = strlen(s1);

char s2[s1_len];
for (int i = 0; i < s1_len; i++) {
    s2[i] = toupper(s1[i]); // "HELLO"
}

char s3[s1_len];
for (int i = 0; i < s1_len; i++) {
    s2[i] = tolower(s1[i]); // "hello"
}

char s4[4];
strncpy(s4, &s1[1], 3); // "ell"
s4[3] = '\0';

char s5[4];
strncpy(s5, &s1[2], 3); // "llo"
s5[3] = '\0';

char c = s1[1];                // 'e'
int  i = strstr(s1, "l") - s1; // 2

C++

#include <algorithm>
#include <string>

string s1 = "Hello";

transform(s1.begin(), s1.end(), s1.begin(), ::toupper);  // "HELLO"
transform(s1.begin(), s1.end(), s1.begin(), ::tolower);  // "hello"

string s4 = s1.substring(1, 3);  // "ell"
string s5 = s1.substring(2);     // "llo"

char c = s1.at(1);         // 'e'
int i = s1.find('l');      // 2

One thing to note, in particular, is that operations on Strings don’t change the original String, but return a new one. All of these method calls above are returning new Strings and the original one is still stored in s1, unchanged.