Java Strings

String is sequence of characters which are make a words. Java programing are provide String class to deal text values. That are defined in the java.lang package. We can declare string object (variable) by using String class.

String name;
String address;

We can assign string text to variable in two ways. By using literals and using new operator.

String name="Java"; //using literals
String address=new String("Everywhere");//using new 

Both given statement are create object of strings and set string literals values. String literals will be defined inside " " double quotes. String object is immutable, so we cannot modified exist specified text contain to string. But there are possible to assign new literals to an String object. For example.

public class MyString {

  public static void main(String[] args) {
    
   String textData="Old Code";
   System.out.println(textData);

   //Assign a new literals to string object
   textData="New Code"; 

   System.out.println(textData);
  }
}

Output

Old Code
New Code

String is collection of character element. Java String class is provide charAt(int) function to get specific character of particular index.

public class MyString {

  public static void main(String[] args) {
    
   String textData="ABCD";
   System.out.println(textData.charAt(0));
   System.out.println(textData.charAt(1));   
   System.out.println(textData.charAt(2));
  }
}

Output

A
B
C

String class methods

String Method example

Concatenating two string

Using a + operator or concat() method are used to combine the value of two literals or two string object value in java programming.

public class MyString {

  public static void main(String[] args) {
    
    String textOne="Java ",textTwo="Programming";
    //concatenating two string object values by + operator
    String test1=textOne + textTwo;
    
    //concatenating two string object values by concat()
    String test2=textOne.concat(textTwo);

    System.out.println(test1);
    System.out.println(test2); 
  } 
}

Output

Java Programming
Java Programming

Compare Two String

When we are compare two string object value in Java Programming, Then there is possible most of programmer are use == (equal to equal to) Operator. But that is not valid when create a string object by using new operator And compare the string object to a constant literals. See this example.

//compare string
public class MyString{
  
  public static void main(String[] args) {
    
    String text1="case1";
    String text2="case1";

    //Case 1 :Compare two normal text variables
    if(text1==text2){
      System.out.println("Case 1 True");
    }else{
      System.out.println("Case 1 False");
    }
    
    String text3=new String("case2");

    //Case 2 : comparing of one string object and text string
    if(text3=="case2"){
      System.out.println("Case 2 True");
    }else{
      System.out.println("Case 2 False");
    }


    String text4=new String("case3");
    String text5=new String("case3");
    
    //case 3 : comparing of two string object
    if(text4==text5){
       System.out.println("Case 3 True");
    }else{
      System.out.println("Case 3 False");
    }
  }
}

Output

Case 1 True
Case 2 False
Case 3 False

So we can use equal() String function to compare two different objects and constant literals value. Comparing of string value using of equal() java function.

//java compare string
public class MyString{
  
  public static void main(String[] args) {
    
    String text1="case1";
    String text2="case1";
    String text3=new String("case2");
    String text4=new String("case3");
    String text5=new String("case3");
    
    //compare value of two string by equals() function
    System.out.println(text1.equals(text2));
    System.out.println(text3.equals("case2"));
    System.out.println(text4.equals(text5));
    System.out.println("case2".equals(text5));

  }
}

Output

true
true
true
false

Split a String in Java

When we are need to split string elements by specific character,digits and symbols to separate. In this situation we can use split() function in java programming. For example.

//split a string in Java
class Execution{
  public int data;
  public static void main(String[] args) {
    String dataVale="10-12-2020";
    //divide string by -
    String[] newData=dataVale.split("-");
    System.out.println(newData[0]); //10
    System.out.println(newData[1]); //12
    System.out.println(newData[2]); //2020
  }
}

10
12
2020

There is an basic example in case we are need to split string in particular limit then we can choose another variant of split(String regex, int limit) function.

//Split a string in Java
class Execution{
 
  public static void main(String[] args) {
    String dataVale="1-2-3-4-5";
    //divide string by -
    String[] splitData=dataVale.split("-",4); //limit 4
    
      for (String item : splitData) {
        System.out.println(item);
    }  
  }
}

1
2
3
4-5

Note that This function are split a string from left to right.

Replace Text In String

When we are need to modify specific character or text value in any string objects. Then we can use replaceAll(String oldText, String newText) method. This method are replacing all oldText value to newText value , And return a new String literals

public class MyString {

  public static void main(String[] args) {
    
   String textData="Learn X to X";

   //Replace letter X to Java
   String newText=textData.replaceAll("X","Java");

   System.out.println(textData); //actual text
   System.out.println(newText); //new converted text

  }
}

Output

Learn X to X
Learn Java to Java

Uppercase and Lowercase conversion

Some case we are need to convert a string data to lowercase and uppercase letters. In this situation we can use toLowerCase() in toUpperCase() methods.

public class MyString {

  public static void main(String[] args) {
    
   String textData="Simple Text";

   
   //lowercase conversion
   System.out.println("Lower Case Text: "+(textData.toLowerCase()));
   //uppercase conversion 
   System.out.println("Upper Case Text: "+(textData.toUpperCase())); 
   //Actual object value
   System.out.println("Given Text: "+textData);
  }
}

Output

Lower Case Text: simple text
Upper Case Text: SIMPLE TEXT
Given Text: Simple Text

Note that both method ( toLowerCase() and toUpperCase() ) are not modified the object value that is returning new Text when is form of lowercase and uppercase letters.

Evaluate string mathematical expression

Generally all math operations are work in numeric values. In case given mathematical equation and expression are in form of string. Then there are very difficult to execute this evaluates logically. We can evaluate in this expression as follows.

//Evaluate string math expression
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
class Execution{

  public static void main(String[] args) {
    ScriptEngineManager sem = new ScriptEngineManager();
    ScriptEngine se = sem.getEngineByName("JavaScript");
    String text = "1000+10*2";
    try{
      //When String text is valid mathematical expression
      System.out.println(se.eval(text)); //1020
    }catch(Exception e){
      System.out.println(e);
    }
  }
}

Output

1020

Convert string to integers in java

parseInt() method are used to convert string text to an integers. note that string text is form of numbers otherwise it will produce an exception. So put this process inside try catch block.

//Java convert string to integers

class Execution{
  
  public static void main(String[] args) {
   
   String text="123";
   int number=0;
   try{
      //convert text value to int
      number=Integer.parseInt(text);
      System.out.println(number);
   }catch(NumberFormatException ex){
      number=0;
      System.out.println("Invalid Text");
   }
 }
}

Output

123

Trim String Text

public class MyString{

  public static void main(String[] args){ 
   
    String text = "   Simple\tTest String   ";
    
    //Replace tab to space
    //And removing spaces in beginning and end of text data
    String trimText=text.trim(); //trim

    System.out.println(text);
    System.out.println(trimText);
  }
}

   Simple  Test String   
Simple  Test String

Substrings String Text

This method are useful to implements new substring.

public class MyString{

  public static void main(String[] args){ 
   
    String text = "Code Keyword A-Z";
      
    String subTextOne=text.substring(5); 
    String subTextTwo=text.substring(5,12);

    System.out.println(text);
    System.out.println(subTextOne);
    System.out.println(subTextTwo);
  }
}

Code Keyword A-Z
Keyword A-Z
Keyword