Kelas Wrapper kanthi rinci

1. Integerkelas

Integeruga apik ing iku kelas, kang tegese iku bisa duwe lapangan lan cara. Lan, mesthi, duwe wong-wong mau. A akèh wong - Welasan wong. Ing kene kita bakal nimbang sing paling dhasar.

Kelas kasebut Integernduweni rong kolom sing ngemot nilai maksimum lan minimal saka intjinis kasebut:

Integer.MAX_VALUE

Integer.MIN_VALUE

Kadhangkala sampeyan pengin nemtokake intnilai sing paling cilik utawa paling gedhe menyang variabel. Kanggo ngindhari kode sampeyan kanthi konstanta sing ora bisa dingerteni, sampeyan bisa nulis iki kanthi cetha kaya ing ngisor iki:

int min = Integer.MIN_VALUE;

min == 0x80000000

Kelas Integeruga duwe sawetara cara sing menarik. Punika:

String Integer.toHexString(int)

String Integer.toBinaryString(int)

String Integer.toOctalString(int)

Integer Integer.valueOf(int i)

Integer Integer.parseInt(String)

Sampeyan sadurunge nemoni cara statis Integer.parseInt(). Ayo kelingan cara kerjane:

int name = Integer.parseInt(string);

Yen senar sing ngemot nomer (mung digit) diterusake menyang parseInt()metode kasebut, bakal ngurai senar kasebut lan ngasilake nomer kasebut.

Liyane saka cara uga migunani. Contone, sawetara bisa ngowahi nomer liwati menyang senar ngemot perwakilan binar, octal utawa heksadesimal saka nomer.

2. Doublekelas

Umumé, Doublekelas padha karo Integerkelas, mung mbungkus a doubletinimbang int. Uga duwe lapangan lan cara sing bakal dadi kapentingan kanggo kita. Coba sawetara:

Kelas kasebut Doublenduweni enem lapangan sing menarik:

double Double.NEGATIVE_INFINITY

double Double.POSITIVE_INFINITY

int Double.MIN_EXPONENT

int Double.MAX_EXPONENT

double Double.MIN_VALUE

double Double.MAX_VALUE

tanpa wates

Yen sampeyan dibagi -1.0dening 0.0, sampeyan entuk infinity negatif. Yen sampeyan dibagi 1.0dening 0.0, sampeyan entuk infinity positif. Ora mung bisa dibagi doublekaro nul, nanging sampeyan uga bisa nggunakake nyimpen asil operasi iki.

Eksponen saka adouble

Ngerteni eksponen iku gampang. Sacara internal, dobel kasusun saka mantissa lan eksponen. Nanging ing kene regane eksponen ora , nanging . Mangkono, yen eksponen mundhak dening , Nilai total nomer bakal pindho.10x2x1

MIN_EXPONENT == -1024, kang tegese , kang kira-kira padha karo2-102410-308

Lan mesthi, Doublekelas kasebut duwe cara sing menarik:

String Double.toHexString(double)

boolean Double.isInfinite(double)

boolean Double.isNaN(double)

Double Double.valueOf(double)

Double Double.parseDouble(String)

Apike, ana isInfinite()cara sing bali trueyen nomer liwati positif utawa negatif tanpa wates.

Cara kasebut isNaN()padha - mriksa manawa nomer sing dilewati yaiku NaN( Not-a-Number , konstanta khusus sing nuduhake nilai sing ora ditemtokake).

3. Characterkelas

Kelas kasebut Charactermenarik utamane amarga akeh metode sarana statis sing ngidini sampeyan mriksa apa karakter kalebu macem-macem kategori.

Tuladha

Character.isAlphabetic(int)

Character.isLetter(char)

Character.isDigit(char)

Character.isSpaceChar(char)

Character.isWhitespace(char)

Character.isLowerCase(char)

Character.isUpperCase(char)

Character.toLowerCase(char)

Character.toUpperCase(char)

Fitur saka metode iki yaiku bisa digunakake karo kabeh aksara sing dikenal: Angka Arab diklasifikasikake minangka digit, lsp.

4. Booleankelas

Jinis kasebut Booleanmeh padha karo booleanjinis. Bentenipun minimal.

Ing ngisor iki kita nuduhake versi kelas sing disederhanakake Boolean:

class Boolean
{
   public static final Boolean TRUE = new Boolean(true);
   public static final Boolean FALSE = new Boolean(false);

   private final boolean value;

   public Boolean(boolean value)
   {
      this.value = value;
   }

   public boolean booleanValue()
   {
      return value;
   }

   public static Boolean valueOf(boolean value)
   {
      return (value ? TRUE : FALSE);
   }
}

Jinis kasebut Booleanduwe rong konstanta (loro kolom):

Boolean.TRUE

true

Boolean.FALSE

false

Sampeyan bisa nggarap dheweke kanthi cara sing padha karo jinis boolean:

if (Boolean.TRUE)
{
}

Boolean a = Boolean.TRUE;
boolean b = Boolean.TRUE;
boolean c = true;

Boolean a = Boolean.TRUE;
Boolean b = Boolean.TRUE;
if (a == b)

Autoboxing kerjane apik ing kene. Tegese sampeyan bisa nggunakake jinis iki kanthi cara sing padha karo jinis boolean- ora ana pitfalls sing kudu diwaspadai.

Boolean a = true;
Boolean b = true;
Boolean c = false;
boolean d = a;

Boolean a = Boolean.valueOf(true);
Boolean b = Boolean.valueOf(true);
Boolean c = Boolean.valueOf(false);
boolean d = a.booleanValue();

Lan ing kene perbandingan booleanlan Booleanjinis:

boolean a = true;
Boolean b = true; // b will be equal to Boolean.TRUE
Boolean c = true; // c will be equal to Boolean.TRUE

a == b; // true (compared by value)
a == c; // true (compared by value)
b == c; // true (compared by reference, but they point to the same object)

Yen sampeyan pancene mbutuhake Booleanobyek independen, mula sampeyan kudu nggawe kanthi jelas:

boolean a = true;
Boolean b = new Boolean(true); // New Boolean object
Boolean c = true; // c will be equal to Boolean.TRUE

a == b; // true (compared by value)
a == c; // true (compared by value)
b == c; // false (compared by reference, and they point to different objects)

Conto liyane, ing ngendi kita bakal nggunakake ing Booleannjero if:

Boolean less = (2 < 3);
if (less)
{
   ...
}

Iki bakal ngumpulake, nanging ora bisa!

Boolean less = null;
if (less)
{
   ...
}

5. Nilai cache sajrone autoboxing

Ana sawetara pitfalls related kanggo jinis pambungkus integer.

Kaya sing wis dingerteni, yen mbandhingake an intlan Integer, Integerdiowahi dadi int:

int a = 5;
Integer b = 5;
if (a == b)
{
   ...
}

int a = 5;
Integer b = Integer.valueOf(5);
if (a == b.intValue())
{
   ...
}

Yen sampeyan mbandhingake rong Integerobyek, ora diowahi dadi ints:

Integer a = 500;
Integer b = 500;
int c = 500;

System.out.println(a == b); // Compared by reference
System.out.println(a == c);
System.out.println(b == c);

false
true
true

a == clan , nanging , amarga nalika kita mbandhingaké lan kita mbandhingaké referensi. Kang ateges apa kita bakal nyana.b == ca != bab

Kaget

Nanging yen kita ngganti 500karo 100, banjur kita entuk asil sing beda banget:

Integer a = 100;
Integer b = 100;
int c = 100;

System.out.println(a == b); // Compared by reference
System.out.println(a == c);
System.out.println(b == c);

true
true
true

Masalah ing kene yaiku obyek anyar ora mesthi digawe sajrone autoboxingInteger . Obyek di-cache kanggo nilai -128liwat 127inklusif.

Kelas kasebut Integernduweni array sing didhelikake sing nyimpen obyek: Integer(-128), Integer(-127), ... Integer(126),Integer(127)

Yen sampeyan nulis Integer x = 128, banjur proses autoboxing nggawe obyek anyar, nanging yen sampeyan nulis Integer x = 127, banjur proses autoboxing njupuk obyek sing wis ana saka cache (saka array).

Yen sampeyan ora pengin Integerobyek kasebut teka saka cache, sampeyan kudu nggawe kanthi jelas kanthi nulis:Integer x = new Integer(127);

Kabeh jinis pambungkus duwe cache kayata: Integer, Long, Byte, Short, Boolean. Kanggo Booleanjinis, TRUElan FALSEnilai-nilai kasebut minangka konstanta, mula uga ana cache.