This blog presents how to convert data types among int, Integer and String.
目录
1. int, Integer and String
1.1 int
Refer to the Java™ Tutorials: Primitive Data Types )
By default, the
int
data type is a 32-bit signed two’s complement integer, which has a minimum value of -231 and a maximum value of 231-1. In Java SE 8 and later, you can use theint
data type to represent an unsigned 32-bit integer, which has a minimum value of 0 and a maximum value of 232-1. Use the Integer class to useint
data type as an unsigned integer. See the section The Number Classes for more information. Static methods likecompareUnsigned
,divideUnsigned
etc have been added to theInteger
class to support the arithmetic operations for unsigned integers.
1.2 Integer
Refer to here.
//java.lang.Object <-- java.lang.Number <--java.lang.Integer //All Implemented Interfaces: Serializable, Comparable<Integer> public final class Integer extends Number implements Comparable<Integer>
The
Integer
class wraps a value of the primitive typeint
in an object. An object of typeInteger
contains a single field whose type isint
.
Note that the ‘int’ type is a primitive , whereas the ‘Integer’ type is an object.
1.3 String
Refer to here.
//java.lang.Object <-- java.lang.String //All Implemented Interfaces: Serializable, CharSequence, Comparable<String> public final class String extends Object implements Serializable, Comparable<String>, CharSequence //for example String str = "abc"; char str[] = {'a', 'b', 'c'}; String str = new String(data);
The
String
class represents character strings. All string literals in Java programs, such as"abc"
, are implemented as instances of this class. Strings are constant; their values cannot be changed after they are created. String buffers support mutable strings. Because String objects are immutable they can be shared.
2. int <–> String
2.1 int to String
There are two ways to convert an int to a String.
//Class Integer static String toString(int i) //Returns a String object representing the specified integer. //Class String public static String valueOf(int i) //Returns the string representation of the int argument. //for example int i = 1234; String str; str = Integer.toString(i); str = String.valueOf(i);
2.2 String to int
public static int parseInt(String s, int radix) throws NumberFormatException //String can be null. To avoid 'java.lang.NumberFormatException: null', int i = str != null ? Integer.parseInt(str) : -1;
3. String <–> Integer
3.1 String to Integer
static Integer valueOf(String s) //Returns an Integer object holding the value of the specified String. // for example String str = "1234"; Integer integer = Integer.valueOf(str) //OR Integer integer = new Integer(str)
3.2 Integer to String
String toString() //Returns a String object representing this Integer's value. //for example Integer integer = new Integer("1234") String str = integer.toString()
4. int <–> Integer
4.1 int to Integer
static Integer valueOf(int i) //Returns an Integer instance representing the specified int value. //for example int i = 1234; Integer integer = Integer.valueOf(i);
4.2 Integer to int
int intValue() //Returns the value of this Integer as an int. //Noted that an Integer can be null. The better way to convert an Integer to an int is: Integer integer = new Integer("1234"); int i = integer != null ? integer.intValue() : -1;赞赏
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