Java StringBuilder.ensureCapacity()

Java StringBuilder.ensureCapacity() – Examples

In this tutorial, we will learn about the Java StringBuilder.ensureCapacity() function, and learn how to use this function to ensure specific capacity for a StringBuilder, with the help of examples.

ensureCapacity(int minimumCapacity)

StringBuilder.ensureCapacity() ensures that the capacity is at least equal to the specified minimum capacity.

If zero or negative value is specified for minimum capacity, ensureCapacity() does nothing.

If minimumCapacity is less than old capacity, ensureCapacity() does nothing.

The new capacity ensureCapacity() allocates is the maximum of

minimumCapacity
Twice old capacity + 2

Syntax

The syntax of ensureCapacity() function is

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ensureCapacity(int minimumCapacity)

where

Parameter	Description
minimumCapacity	Then minimum desired capacity for the StringBuilder.

Returns

The function returns void.

Example 1 – ensureCapacity(minimumCapacity)

In this example, we will initialize an empty StringBuilder, and call ensureCapacity() on this StringBuilder with a minimumCapacity of 20.

Java Program

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public class Example { 
    public static void main(String[] args) { 
        StringBuilder stringBuilder = new StringBuilder();
        System.out.println("Old capacity : " + stringBuilder.capacity());
        
        int minimumCapacity = 20;
        stringBuilder.ensureCapacity(minimumCapacity);
        System.out.println("New capacity : " + stringBuilder.capacity());
    }
}

Output

Old capacity : 16
New capacity : 34

Explanation

New capacity = maximum of (minimumCapacity, twice old capacity + 2)
             = maximum of (20, 2 * 16 + 2)
             = maximum of (20, 34)
             = 34

Example 2 – ensureCapacity() – minimumCapacity < old capacity

In this example, we will specify a minimumCapacity such that it is less than the old capacity. ensureCapacity() does nothing and return.

Java Program

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public class Example { 
    public static void main(String[] args) { 
        StringBuilder stringBuilder = new StringBuilder();
        System.out.println("Old capacity : " + stringBuilder.capacity());
        
        int minimumCapacity = 10;
        stringBuilder.ensureCapacity(minimumCapacity);
        System.out.println("New capacity : " + stringBuilder.capacity());
    }
}

Output

Old capacity : 16
New capacity : 16

Example 3 – ensureCapacity(minimumCapacity)

In this example, we will specify a negative value for minimumCapacity. ensureCapacity() does nothing and return.

Java Program

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public class Example { 
    public static void main(String[] args) { 
        StringBuilder stringBuilder = new StringBuilder();
        System.out.println("Old capacity : " + stringBuilder.capacity());
        
        int minimumCapacity = -2;
        stringBuilder.ensureCapacity(minimumCapacity);
        System.out.println("New capacity : " + stringBuilder.capacity());
    }
}

Output

Old capacity : 16
New capacity : 16

Example 4 – ensureCapacity(minimumCapacity)

In this example, we will provide a minimumCapacity of 200, which is greater than twice old capacity + 2. Now, ensureCapacity() will increase the capacity of this StringBuilder sequence to specified minimumCapacity of 200.

Java Program

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public class Example { 
    public static void main(String[] args) { 
        StringBuilder stringBuilder = new StringBuilder();
        System.out.println("Old capacity : " + stringBuilder.capacity());
        
        int minimumCapacity = 200;
        stringBuilder.ensureCapacity(minimumCapacity);
        System.out.println("New capacity : " + stringBuilder.capacity());
    }
}

Output

Old capacity : 16
New capacity : 200

Conclusion

In this Java Tutorial, we have learnt the syntax of Java StringBuilder.ensureCapacity() function, and also learnt how to use this function with the help of examples.

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Java StringBuilder.ensureCapacity() – Syntax & Examples