HashMap原始碼分析jdk1 8

hashmap作為一種最常用的集合型別之一，他的實現是用的雜湊表，在這就不進行雜湊表詳細的解釋。為解決雜湊表的衝突問題，hashmap即是採用了鏈位址法，也就是陣列+鍊錶的方式。廢話不多說，我們還是通過原始碼來進行hashmap的詳解。

組成hashmap的基本單元node節點

/**
*node節點的定義
*/static
class nodeimplements map.entry
}

而為了實現鍊錶加陣列的結構，它定義了這麼乙個變數 transient node table; 這個變數其實就代表了hashmap的主體，接下來看下他如何實現hashmap的功能。讓我們再來看hashmap的原始碼

hashmap中定義了這麼幾個常量，正如他的注釋所講。在這就不行翻譯了。

/**
* the default initial capacity - must be a power of two.
*/static
final
int default_initial_capacity = 1 << 4; //
aka 16
/*** the maximum capacity, used if a higher value is implicitly specified
* by either of the constructors with arguments.
* must be a power of two <= 1<<30.
*/static
final
int maximum_capacity = 1 << 30;
/*** the load factor used when none specified in constructor.
*/static
final
float default_load_factor = 0.75f;

了解這些我們再來看hashmap的主要**

final v putval(int hash, k key, v value, boolean
onlyifabsent,
boolean
evict) 
if (e.hash == hash &&((k = e.key) == key || (key != null &&key.equals(k))))
break
;                    p =e;}}
if (e != null) 
}++modcount;
if (++size >threshold)
resize();
afternodeinsertion(evict);
return
null
;    }
/*** initializes or doubles table size.  if null, allocates in
* accord with initial capacity target held in field threshold.
* otherwise, because we are using power-of-two expansion, the
* elements from each bin must either stay at same index, or move
* with a power of two offset in the new table.** 
@return
the table
*/final node resize() 
else
if ((newcap = oldcap << 1) < maximum_capacity &&oldcap >=default_initial_capacity)
newthr = oldthr << 1; //
double threshold
}        
else
if (oldthr > 0) //
initial capacity was placed in threshold
newcap =oldthr;
else 
if (newthr == 0) 
threshold =newthr;
@suppresswarnings()
node
newtab = (node)new
node[newcap];
table =newtab;
if (oldtab != null
)                             
else
} while ((e = next) != null
);                        
if (lotail != null
)                         
if (hitail != null
)                     }}}
}return
newtab;
}

HashMap原始碼分析jdk1 8

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HashMap原始碼分析 JDK1 8

HashMap原始碼分析jdk1 8

分析HashMap 的 JDK 原始碼

hashmap原始碼分析jdk8

HashMap原始碼分析 JDK1 8

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