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    Java String Methods


    Java StringBuffer class

    Java StringBuffer class is used to create mutable (modifiable) string. The StringBuffer class in java is same as String class except it is mutable i.e. it can be changed.

    Note: Java StringBuffer class is thread-safe i.e. multiple threads cannot access it simultaneously. So it is safe and will result in an order.

    Important Constructors of StringBuffer class

    Constructor Description
    StringBuffer() creates an empty string buffer with the initial capacity of 16.
    StringBuffer(String str) creates a string buffer with the specified string.
    StringBuffer(int capacity) creates an empty string buffer with the specified capacity as length.

    Important methods of StringBuffer class

    Modifier and Type Method Description
    public synchronized StringBuffer append(String s) is used to append the specified string with this string. The append() method is overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
    public synchronized StringBuffer insert(int offset, String s) is used to insert the specified string with this string at the specified position. The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int, float), insert(int, double) etc.
    public synchronized StringBuffer replace(int startIndex, int endIndex, String str) is used to replace the string from specified startIndex and endIndex.
    public synchronized StringBuffer delete(int startIndex, int endIndex) is used to delete the string from specified startIndex and endIndex.
    public synchronized StringBuffer reverse() is used to reverse the string.
    public int capacity() is used to return the current capacity.
    public void ensureCapacity(int minimumCapacity) is used to ensure the capacity at least equal to the given minimum.
    public char charAt(int index) is used to return the character at the specified position.
    public int length() is used to return the length of the string i.e. total number of characters.
    public String substring(int beginIndex) is used to return the substring from the specified beginIndex.
    public String substring(int beginIndex, int endIndex) is used to return the substring from the specified beginIndex and endIndex.

    What is mutable string

    A string that can be modified or changed is known as mutable string. StringBuffer and StringBuilder classes are used for creating mutable string.

    1) StringBuffer append() method

    The append() method concatenates the given argument with this string.

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    2) StringBuffer insert() method

    The insert() method inserts the given string with this string at the given position.

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    3) StringBuffer replace() method

    The replace() method replaces the given string from the specified beginIndex and endIndex.

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    4) StringBuffer delete() method

    The delete() method of StringBuffer class deletes the string from the specified beginIndex to endIndex.

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    5) StringBuffer reverse() method

    The reverse() method of StringBuilder class reverses the current string.

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    6) StringBuffer capacity() method

    The capacity() method of StringBuffer class returns the current capacity of the buffer. The default capacity of the buffer is 16. If the number of character increases from its current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

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    7) StringBuffer ensureCapacity() method

    The ensureCapacity() method of StringBuffer class ensures that the given capacity is the minimum to the current capacity. If it is greater than the current capacity, it increases the capacity by (oldcapacity*2)+2. For example if your current capacity is 16, it will be (16*2)+2=34.

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