Posted on: July 27, 2006 at 12:00 AM
Java: Summary - java.util.StringBuilder and java.util.StringBuffer
In this section you will learn about java.util.StringBuilder and java.util.StringBuffer classes.
We will also see the different way of creating the object of java.util.StringBuilder class.
Strings are immutable (can't be changed), so manipulating strings often causes many temporary string objects to be created, which can be quite inefficient.
StringBuilder (or StringBuffer) are better choices in these cases.
Their toString()
method can be used get a String value.
It isn't necessary to create them with a specific size, it will expand as necessary.
Many StringBuilder methods return the same StringBuilder so that the call chaining style of programming can be used.
StringBuilder is basically identical to the older StringBuffer,
but is slightly faster because it isn't synchronized.
Following table summarizes the Constructors:
| Constructors | ||
| sb = | new StringBuilder() | Creates empty StringBuilder |
| sb = | new StringBuffer(n) | Creates empty StringBuilder with initial capacity n. |
| sb = | new StringBuffer(s) | Creates StringBuilder with value initialized to String s. |
| Length | ||
| i = | sb.length() | Length of the current contents of sb. |
| Modifying the content - These methods return the original StingBuilder to allow call chaining. | ||
| sb = | sb.append(x) | Appends x (char, int, String, ...) to end of sb. |
| sb = | sb.insert(offset, x) | Inserts x (char, int, String, ...) at position offset. |
| sb = | sb.setCharAt(index, c) | Replaces char at index with c |
| sb = | sb.delete(beg, end) | Deletes chars at index beg thru end. |
| sb = | sb.reverse() | Reverses the contents. |
| sb = | sb.replace(beg, end, s) | Replaces characters beg thru end with s. |
| Getting parts | ||
| c = | sb.charAt(i) | char at position i in sb. |
| s = | sb.substring(i) | substring from index i to the end of sb. |
| s = | sb.substring(i, j) | substring from index i to BEFORE index j of sb. |
| Misc | ||
| s = | sb.toString() | Returns a String for the contents of sb. |
| Searching -- Note: All "indexOf" methods return -1 if the string/char is not found | ||
| i = | sb.indexOf(s) | index of the first occurrence of String s in s. |
| i = | sb.indexOf(s, i) | index of String s at or after position i in sb. |
| i = | sb.lastIndexOf(s) | index of last occurrence of s in sb. |
| i = | sb.lastIndexOf(s, i) | index of last occurrence of s on or before i in sb. |
| Comparison (note: use this instead of == and !=) | ||
| b = | sb.equals(sb2) | true if the two StringBuffers contain equal values |