KinChungE

但係好奇一問, 點解 Java 仲係慢過 C++?
snoopy11hk 發表於 2013-4-4 17:40

因為Java唔係run native code, 要行VM

snoopy11hk

因為Java唔係run native code, 要行VM
KinChungE 發表於 2013-4-4 17:56

    問錯野, 應該係:點解 Java 食 RAM 過 C++ 咁多
如果話 Java 係有用 Pointer, 應該可以同 C++ 等同咁濟, 但點解事實又唔係呢?
Android 而家 D 機都用緊 2GB RAM, Windows 2GB ram 行得好smooth 下, 但 Android 都話唔夠 RAM?

KinChungE

問錯野, 應該係:點解 Java 食 RAM 過 C++ 咁多
如果話 Java 係有用 Pointer, 應該可以同 C++ 等同咁 ...
snoopy11hk 發表於 2013-4-4 18:11

因為行VM

Jackass_TMxCK

問錯野, 應該係:點解 Java 食 RAM 過 C++ 咁多
如果話 Java 係有用 Pointer, 應該可以同 C++ 等同咁 ...
snoopy11hk 發表於 4/4/2013 06:11 PM

    Java同Flash/Air都係行虛擬程式，virtual machine黎行

faiwaic

你估java裏面果個 NullPointerException 個名點黎架呢?
Java / .Net 裏面所謂O既reference, functi ...
LoneGumMan 發表於 2013-4-4 01:10

    雖然 我唔係太了解java, 但 .Net support C 既 function, 而 C 有pointer 的

LoneGumMan

.Net CLR 設計O既其中一個criteria係可以同native platform interop. Java 都有 JNI.

因為C 基本上有一個全世界都理解同埋同意左O既 calling convention, call native code 唔係咁大不了. 只要 GEN 到o岩O既function setup, jmp 到O岩O既address, 下一個 instruction 就係native code, return 返黎, 睇得明個 memory layout, 恭喜晒, 你 call 左native function!

要記住一樣野, pointer 真係唔係咁大不了, 佢只係一個 address. pointer to pointer, pointer to pointer to pointer ... etc 說穿了其實都係同一個mechanism,只不過多左 n 咁多個 level of indirection. 仲有function pointer, memory function pointer ... 唔好俾佢地嚇怕.

LoneGumMan

其實pointer 搞到咁難用咁樣
點解唔做返要自己copy 份新出黎，而default 用左pass by value
有無人知當初 ...
DarkHero 發表於 2013-4-4 12:51

當你要落到 bare metal, 就一定要掂到 memory 同address.

memory address to an integer, memory address of memory address to an integer .. 好長, pointer to integer, pointer of pointer to integer 易讀D :) 同埋, 當你響黑板度畫公仔O既時候, pointer 一定係畫箭咀, 所以叫做pointer囉.

snoopy11hk

當你要落到 bare metal, 就一定要掂到 memory 同address.

memory address to an integer, memory address  ...
LoneGumMan 發表於 2013-4-5 00:00

    其實 pointer 好易, 只要你習慣左就咩問題都無

LoneGumMan

雖然 我唔係太了解java, 但 .Net support C 既 function, 而 C 有pointer 的  ...
faiwaic 發表於 2013-4-4 22:34

如果你睇番JAVA o既歷史, 你會發現其實而家叫O既所謂"reference" 原本係就咁叫做POINTER, 因為佢根本就係一個POINTER :) 到後來, 因為 VM implementation 令到佢同一般POINTER 有D 唔同, 為左唔好令人誤會, 所以改名 (同埋marketing..sun 想人地覺得佢好似先進D)

g2david

Pointer 由Assembler 開始, Pascel, 到C, C++ 全部都有. 因為初學者學習Pointer時面對困難, 簡化為Reference 同Garbage Collection.

你有意識去學是很好. 未來可能己是low level stuff.