Strings API

Question 1

What does charAt(i) do?

Answer 1

charAt(int index)

Returns the char value at the specified index.

Question 2

What do codePointAt(i), codePointBefore(i), codePointCount(i, j) do?

Answer 2

codePointAt(int index)
Returns the character (Unicode code point) at the specified index.

codePointBefore(int index)
Returns the character (Unicode code point) before the specified index.

int	codePointCount(int beginIndex, int endIndex)
Returns the number of Unicode code points in the specified text range of this String.

Question 3

What do compareTo(s), compareToIgnoreCase(s) do?

Answer 3

int compareTo(String anotherString)
Compares two strings lexicographically.

int compareToIgnoreCase(String str)
Compares two strings lexicographically, ignoring case differences.

Question 4

What does concat(s) do?

Answer 4

String concat(String str)
Concatenates the specified string to the end of this string.

Question 5

What does contains(cs) do?

Answer 5

boolean	contains(CharSequence s)
Returns true if and only if this string contains the specified sequence of char values.

Question 6

What do copyValueOf(ca), copyValueOf(ca, i, j) do?

Answer 6

static String copyValueOf(char[] data)
Returns a String that represents the character sequence in the array specified.

static String copyValueOf(char[] data, int offset, int count)
Returns a String that represents the character sequence in the array specified.

Question 7

What does endsWith(s) do?

Answer 7

boolean endsWith(String suffix)
Tests if this string ends with the specified suffix.

Question 8

What do equals(o), equalsIgnoreCase(s), contentEquals(cs), contentEquals(sb) do?

Answer 8

boolean equals(Object anObject)
Compares this string to the specified object.

boolean equalsIgnoreCase(String anotherString)
Compares this String to another String, ignoring case considerations.

boolean	contentEquals(CharSequence cs)
Compares this string to the specified CharSequence.

boolean	contentEquals(StringBuffer sb)
Compares this string to the specified StringBuffer.

Question 9

What do format(l, sf, oa), format(sf, oa) do?

Answer 9

static String format(Locale l, String format, Object… args)
Returns a formatted string using the specified locale, format string, and arguments.

static String format(String format, Object… args)
Returns a formatted string using the specified format string and arguments.

Question 10

What do getBytes(), getBytes(charset), getBytes(s) do?

Answer 10

byte[] getBytes()
Encodes this String into a sequence of bytes using the platform’s default charset, storing the result into a new byte array.

byte[] getBytes(Charset charset)
Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.

byte[] getBytes(String charsetName)
Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.

void	getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
Deprecated. 
This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the getBytes() method, which uses the platform's default charset.

Question 11

What does hashCode() do?

Answer 11

int hashCode()
Returns a hash code for this string.

Question 12

What do indexOf(c), indexOf(c,j), indexOf(s), indexOf(s, i) do?

Answer 12

int	indexOf(int ch)
Returns the index within this string of the first occurrence of the specified character.

int	indexOf(int ch, int fromIndex)
Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.

int	indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.

int	indexOf(String str, int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.

Question 13

What does intern() do?

Answer 13

String intern()
Returns a canonical representation for the string object.

Question 14

What does isEmpty() do?

Answer 14

boolean isEmpty()
Returns true if, and only if, length() is 0.

Question 15

What do lastIndexOf(c), lastIndexOf(c,i), lastIndexOf(s), lastIndexOf(s, i) do?

Answer 15

int	lastIndexOf(int ch)
Returns the index within this string of the last occurrence of the specified character.

int	lastIndexOf(int ch, int fromIndex)
Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.

int	lastIndexOf(String str)
Returns the index within this string of the last occurrence of the specified substring.

int	lastIndexOf(String str, int fromIndex)
Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.

Question 16

What does length() do?

Answer 16

int length()
Returns the length of this string.

Question 17

What do matches(srex), regionMatches(true, i, s, j, k) do?

Answer 17

boolean	matches(String regex)
Tells whether or not this string matches the given regular expression.

boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
Tests if two string regions are equal.

Question 18

What does offsetByCodePoints(i, j) do?

Answer 18

int offsetByCodePoints(int index, int codePointOffset)
Returns the index within this String that is offset from the given index by codePointOffset code points.

Question 19

What do replace(ch, ch), replace(cs, cs), replaceFirst(srex, s), replaceAll(srex, s) do?

Answer 19

String replace(char oldChar, char newChar)
Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
String replace(CharSequence target, CharSequence replacement)
Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.

String	replaceAll(String regex, String replacement)
Replaces each substring of this string that matches the given regular expression with the given replacement.

String	replaceFirst(String regex, String replacement)
Replaces the first substring of this string that matches the given regular expression with the given replacement.

Question 20

What do split(srex), split(srex, i) do?

Answer 20

String[] split(String regex)
Splits this string around matches of the given regular expression.

String[] split(String regex, int limit)
Splits this string around matches of the given regular expression.

Question 21

What do startsWith(s), startsWith(s,i) do?

Answer 21

boolean	startsWith(String prefix)
Tests if this string starts with the specified prefix.

boolean	startsWith(String prefix, int toffset)
Tests if the substring of this string beginning at the specified index starts with the specified prefix.

Question 22

What does subSequence(i,j) do?

Answer 22

CharSequence subSequence(int beginIndex, int endIndex)
Returns a new character sequence that is a subsequence of this sequence.

Question 23

What do substring(i), substring(i,j) do?

Answer 23

String	substring(int beginIndex)
Returns a new string that is a substring of this string.

String	substring(int beginIndex, int endIndex)
Returns a new string that is a substring of this string.

Question 24

What does toCharArray() do?

Answer 24

char[] toCharArray()

Converts this string to a new character array.

Question 25

What do toLowerCase(), toLowerCase(locale), toUpperCase(), toUpperCase(locale) do?

Answer 25

String	toLowerCase()
Converts all of the characters in this String to lower case using the rules of the default locale.

String	toLowerCase(Locale locale)
Converts all of the characters in this String to lower case using the rules of the given Locale.

String	toUpperCase()
Converts all of the characters in this String to upper case using the rules of the default locale.

String	toUpperCase(Locale locale)
Converts all of the characters in this String to upper case using the rules of the given Locale.

Question 26

What does toString() do?

Answer 26

String toString()
This object (which is already a string!) is itself returned.

Question 27

What does trim() do?

Answer 27

String trim()
Returns a copy of the string, with leading and trailing whitespace omitted.

Question 28

What does valueOf(c), valueOf(ca), valueOf(ca, i, j), valueOf(d), valueOf(f), valueOf(i), valueOf(l), valueOf(o) do?

Answer 28

static String valueOf(boolean b)
Returns the string representation of the boolean argument.
static String valueOf(char c)
Returns the string representation of the char argument.
static String valueOf(char[] data)
Returns the string representation of the char array argument.
static String valueOf(char[] data, int offset, int count)
Returns the string representation of a specific subarray of the char array argument.
static String valueOf(double d)
Returns the string representation of the double argument.
static String valueOf(float f)
Returns the string representation of the float argument.
static String valueOf(int i)
Returns the string representation of the int argument.
static String valueOf(long l)
Returns the string representation of the long argument.
static String valueOf(Object obj)
Returns the string representation of the Object argument.

Question 29

What does getChars(i, j, ca, k) do?

Answer 29

void	getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
Copies characters from this string into the destination character array.