How do you replace one string in a text file in Java?

How do you replace one string in a text file in Java?

Step 1 : Create a File object by passing the path of the file to be modified. Step 2 : Initialize oldContent with an empty string. This String object will hold all the old content of the input text file. Step 3 : Create BufferedReader object to read the input text file line by line.

How do I replace a string in a file?

Find and replace text within a file using sed command

  1. Use Stream EDitor (sed) as follows:
  2. sed -i ‘s/old-text/new-text/g’ input.
  3. The s is the substitute command of sed for find and replace.
  4. It tells sed to find all occurrences of ‘old-text’ and replace with ‘new-text’ in a file named input.

How do you overwrite a line in a text file in Java?

Invoke the replaceAll() method on the obtained string passing the line to be replaced (old line) and replacement line (new line) as parameters. Instantiate the FileWriter class. Add the results of the replaceAll() method the FileWriter object using the append() method.

How do you replace a substring in a string?

Algorithm to Replace a substring in a string

  1. Input the full string (s1).
  2. Input the substring from the full string (s2).
  3. Input the string to be replaced with the substring (s3).
  4. Find the substring from the full string and replace the new substring with the old substring (Find s2 from s1 and replace s1 by s3).

How do you convert Chararray to string?

Use the valueOf() method in Java to copy char array to string. You can also use the copyValueOf() method, which represents the character sequence in the array specified. Here, you can specify the part of array to be copied.

How do I find and replace a character in a string in Java?

Java String replace(char old, char new) method example

  1. public class ReplaceExample1{
  2. public static void main(String args[]){
  3. String s1=”javatpoint is a very good website”;
  4. String replaceString=s1.replace(‘a’,’e’);//replaces all occurrences of ‘a’ to ‘e’
  5. System.out.println(replaceString);
  6. }}

How can you replace all occurrences of the letter?

To replace all occurrences of a substring in a string by a new one, you can use the replace() or replaceAll() method:

  1. replace() : turn the substring into a regular expression and use the g flag.
  2. replaceAll() method is more straight forward.

What is difference between replace and replaceAll in Java?

The difference between replace() and replaceAll() method is that the replace() method replaces all the occurrences of old char with new char while replaceAll() method replaces all the occurrences of old string with the new string.

How do you replace words in Java?

To replace all words with another String using Java Regular Expressions, we need to use the replaceAll() method. The replaceAll() method returns a String replacing all the character sequence matching the regular expression and String after replacement.

How do you modify a string in Java?

Thus, to modify them we use the following methods;

  1. substring(): Using this method, you can extract a part of originally declared string/string object.
  2. concat(): Using this function you can concatenate two strings.
  3. replace(): This method is used to modify the original string by replacing some characters from it.

Can you change the value of a string?

While Strings are immutable, you can re-assign a String variable. Immutable means that you cannot change a String itself not that you cannot reassign what the variable that was pointing to its value now is.

Is it possible to update a string object without using introspection )?

Strings are immutable so you cannot change the value of an already created string. The String object is immutable in Java so any changes create a new String object.

How many string objects are created in the heap when this method is invoked?

The answer is: 2 String objects are created. str and str2 both refer to the same object.

Which two methods are needed to implement use an object as a key in HashMap?

In order to use any object as Key in HashMap, it must implements equals and hashcode method in Java.

Which method is used to compare two strings ignoring the case?


Is string pool part of heap?

A string constant pool is a separate place in the heap memory where the values of all the strings which are defined in the program are stored. When we declare a string, an object of type String is created in the stack, while an instance with the value of the string is created in the heap.

What is the difference between String [] and string?

String[] and String… are the same thing internally, i. e., an array of Strings. The difference is that when you use a varargs parameter ( String… ) you can call the method like: public void myMethod( String… foo ) { // do something // foo is an array (String[]) internally System.

What is the difference between creating string as new () and literal?

At a high level, both are the String objects, but the main difference comes from the point that new() operator always creates a new String object. Also, when we create a String using literal – it is interned. In this example, the String objects will have the same reference.

What is string pool with example?

String pool is an implementation of the String Interring Concept. String Interning is a method that stores only a copy of each distinct string literal. The distinct values are stored in the String pool. String pool is an example of the Flyweight Design Pattern.

What is the use of string pool?

String Pool is a storage area in Java heap. String allocation, like all object allocation, proves to be a costly affair in both the cases of time and memory. The JVM performs some steps while initializing string literals to increase performance and decrease memory overhead.

Where is string pool stored?

Strings are stored on the heap area in a separate memory location known as String Constant pool. String constant pool: It is a separate block of memory where all the String variables are held. String str1 = “Hello”; directly, then JVM creates a String object with the given value in a String constant pool.

What’s the difference between comparison done by equals method and == operator?

We can use == operators for reference comparison (address comparison) and . equals() method for content comparison. In simple words, == checks if both objects point to the same memory location whereas . equals() evaluates to the comparison of values in the objects.

What is the Hashcode () and equals () used for?

The hashcode() method returns the same hash value when called on two objects, which are equal according to the equals() method. And if the objects are unequal, it usually returns different hash values.

Is equal a method?

The equals method implements an equivalence relation on non-null object references: It is reflexive: for any non-null reference value x , x. equals(x) should return true . It is symmetric: for any non-null reference values x and y , x.

How do you override equals?

The String class overrides the equals method it inherited from the Object class and implemented logic to compare the two String objects character by character. The reason the equals method in the Object class does reference equality is because it does not know how to do anything else.

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