うらがみさんアドバイス解析〜リテラルはGCされない〜

by ihcomega56

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͏Β͕Έ͞Μͷ ΞυόΠεղੳୈ஄

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͏Β͕Έ͞Μͱ͍͑͹ ઌੜͷΑ͏ͳଘࡏʂ

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͏Β͕Έ͞Μͱ͍͑͹

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࠷ۙͩͱ DBTFDMBTTͷ ·ͩΑ͘Θ͔ͬͯͳ͍ GMBU.BQͷJNQMJDJUDPOWFSUFS ݁ߏΘ͔ͬͨ ˞4DBMB

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ಛ௃ /PUPOMZઆ໌ #VUBMTPίʔυ

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ࠓ೔͸ ੲ͍͍ͨͩͨίʔυΛ ͣͬͱ์ஔͯ͠෼͔Βͣʹ͍ͨͷͰ ࠓߋղੳͨ͠

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࣌͸ ύʔϑΣΫτ+BWB

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ٙ໰

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ղ౴

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͏Β͕Έ͞ΜʹΑΔ࣮ݧ IUUQTHJTUHJUIVCDPNCBDLQBQFSEBGFGGFCF

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಺༰ wϦςϥϧ wOFXͨ͠΍ͭ wJOUFSOͨ͠΍ͭ wϦςϥϧͦͷ wϦςϥϧͦͷͷΫϥεϩʔμʔ wϦςϥϧͦͷͷΫϥε wϦςϥϧͦͷͷϑΟʔϧυ ($͞ΕΔͷ͔ʁ

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಺༰ wϦςϥϧ wOFXͨ͠΍ͭ wJOUFSOͨ͠΍ͭ wϦςϥϧͦͷ wϦςϥϧͦͷͷΫϥεϩʔμʔ wϦςϥϧͦͷͷΫϥε wϦςϥϧͦͷͷϑΟʔϧυ ͜͜ͷ෦෼Λ௥ͬͨ

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ݴ͍༁ શ෦ग़དྷͳ͔ͬͨͷʹ͸ཧ༝͕ ޙड़

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͍ͬͯΈΑ͏ wϦςϥϧ wOFXͨ͠΍ͭ wJOUFSOͨ͠΍ͭ

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ͦ΋ͦ΋ JOUFSOͬͯͳΜ͚ͩͬ

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JOUFSOϝιου͕ݺͼग़͞Εͨͱ͖ʹɺFRVBMT 0CKFDU ϝιο υʹΑͬͯ͜ͷ4USJOHΦϒδΣΫτʹ౳͍͠ͱ൑ఆ͞ΕΔจࣈ ྻ͕ϓʔϧʹ͢Ͱʹ͋ͬͨ৔߹͸ɺϓʔϧ಺ͷ֘౰͢Δจࣈྻ ͕ฦ͞Ε·͢ɻ ͦ͏Ͱͳ͍৔߹͸ɺ͜ͷ4USJOHΦϒδΣΫτ͕ϓʔϧʹ௥Ճ͞ Εɺ͜ͷ4USJOHΦϒδΣΫτ΁ͷࢀর͕ฦ͞Ε·͢ɻ JOUFSO +BWB%PDΑΓ

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จࣈྻϦςϥϧΛએݴ͢Δͱ 4USJOHϓʔϧͬͯͱ͜ʹอ࣋͞ΕΔ ϓʔϧ

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จࣈྻϦςϥϧΛએݴ͢Δ౓ʹ 4USJOHϓʔϧͷத਎Λ֬ೝͯ͠ ಉ͡จࣈྻ͕͋Ε͹ͦͷࢀরΛ࢖͍ճ͢͠ ͳ͚Ε͹৽͘͠࡞ͬͯอ࣋͢ΔΒ͍͠ ͱ͍͏͔

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ͯ͞ ؾΛऔΓ௚ͯ͠ ίʔυղੳͩͬ ·ͣ͸ ͭͷΠϯελϯεΛ ੜ੒͠Α͏

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ΠϯελϯεΛੜ੒͢Δ wϦςϥϧ wOFXͨ͠΍ͭ wJOUFSOͨ͠΍ͭ

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ΠϯελϯεΛੜ੒͢Δ

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ΠϯελϯεΛੜ੒͢Δ •”aaa” •new String(”bbb”) •new String(new char[] { ‘c’,’c’,’c’ }).intern()

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Μʁ new String(new char[] { ‘c’,’c’,’c’ }).intern() DIBSʜ ϓʔϧʹ௥Ճ͢ΔλΠϛϯάΛ JOUFSO ͕ݺͼग़͞Εͨͱ͖ OPUϦςϥϧ͕એݴ͞Εͨͱ͖ ʹ ͍͔ͨ͠Β͔ͳʁʁʁ

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Μʁ new String(new char[] { ‘c’,’c’,’c’ }).intern() DIBSʜ ϓʔϧʹ௥Ճ͢ΔλΠϛϯάΛ JOUFSO ͕ݺͼग़͞Εͨͱ͖ OPUϦςϥϧ͕એݴ͞Εͨͱ͖ ʹ ͍͔ͨ͠Β͔ͳʁʁʁ ਖ਼ղͰͨ͠ ൃදޙʹ௥Ճͨ͠εϥΠυ

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ͯ͞ ؾΛऔΓ௚ͯ͠ ίʔυղੳͩͬ ࣍͸ ࡞ͬͨΠϯελϯε͕ ($͞ΕΔ͔֬ೝ͠Α͏

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ྲྀΕ ($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($ͷର৅ͱ͢Δ ͕Μ͹ͬͯ($͢Δ ($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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ྲྀΕ

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($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($ͷର৅ͱ͢Δ ͕Μ͹ͬͯ($͢Δ ($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ

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($͞Ε͔ͨ֬ೝ͢Δํ๏ ͷͪ΄Ͳɾɾɾ

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($ͷର৅ͱ͢Δ ($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($ͷର৅ͱ͢Δ ͕Μ͹ͬͯ($͢Δ ($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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͜Ε஌ͬͯΔʂ OVMMΛ୅ೖ͢ΔΜͰ͠ΐ͏ʁ

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($ͷର৅ͱ͢Δ

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($ͷର৅ͱ͢Δ

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($ͷର৅ͱ͢Δ

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ڧࢀরʁ ͳΜͧ

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ུ ऑࢀরΦϒδΣΫτ͸ɺͦͷऑࢀরΦϒδΣΫτͷϦϑΝ Ϩϯτ͕ϑΝΠφϥΠζՄೳʹͳΓɺϑΝΠφϥΠζ͞Εɺͦ ͯ͠࠶ੜ͞ΕΔ͜ͱΛ્ࢭ͢Δ͜ͱ͸͋Γ·ͤΜɻ ͋Δ࣌఺ͰɺΦϒδΣΫτ͕ऑ౸ୡՄೳͰ͋ΔͱɺΨϕʔδί ϨΫλ͕൑அͨ͠ͱ͠·͢ɻͦͷ࣌఺ͰɺΨϕʔδίϨΫλ͸ɺ ͦͷΦϒδΣΫτ΁ͷऑࢀর͢΂ͯͱɺڧࢀর͓Αͼιϑτࢀ রͷνΣʔϯΛܦ༝ͯͦ͠ͷΦϒδΣΫτʹ౸ୡͰ͖ΔΑ͏ͳɺ ΄͔ͷऑ౸ୡՄೳͳΦϒδΣΫτ΁ͷऑࢀর͢΂ͯΛɺݪࢠత ʹΫϦΞ͠·͢ɻಉ࣌ʹɺΨϕʔδίϨΫλ͸Ҏલʹऑ౸ୡՄ ೳͳΦϒδΣΫτ͕͢΂ͯϑΝΠφϥΠζՄೳͰ͋Δ͜ͱΛએ ݴ͠·͢ɻಉ࣌ʹ·ͨ͸͋ͱͰɺΨϕʔδίϨΫλ͸ɺࢀর Ωϡʔʹొ࿥͞Ε͍ͯΔͦΕΒͷ৽͘͠ΫϦΞ͞ΕͨऑࢀরΛ ΩϡʔʹೖΕ·͢ɻ ऑࢀর +BWB%PDΑΓ

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ऑࢀর +BWB%PDΑΓ

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ڧࢀরɾऑࢀর ͻͩ͠·͞ΜϖʔδΛࢀߟʹ ڧࢀরɿ ଟ෼ී௨ͷࢀরΛࢦ͢ ऑࢀরɿ ʮऑࢀরʹͯ͠อ࣋͢Δͱɺ ଞͷ௨ৗͷࢀর͕શͯແ͘ͳΕ͹ɺ ($ͷର৅ʹͳΔʯΒ͍͠ɾɾɾ

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ɾɾɾʁ ʮଞͷ௨ৗͷࢀর͕શͯແ͘ͳΕ͹ɺ ($ͷର৅ʹͳΔʯʁ ͲͷΠϯελϯε΋ͦ͏ͩͱࢥͬͯͨ ऑࢀর͡Όͳ͍΋ͷ͸($ͷର৅Ͱͳ͍ʁ ҧ͍͕Α͘෼͔Βͳ͍ͷ͚ͩͲ ऑࢀরͩͱ($ͷର৅ͱ͍͏͜ͱ͸ ͔֬ͬΆ͍ ࡶ

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ɾɾɾʁ ऑࢀরͷ৔߹͸ ࢀর͕͋ͬͯ΋($ͷର৅ʹͳΔ ͦ͏Ͱ͢ Ωϟογϡͱ͔ʹ࢖͏Β͍͠ ൃදޙʹ௥Ճͨ͠εϥΠυ

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ͯ͞ ؾΛऔΓ௚ͯ͠ ίʔυղੳͩͬ ଓ͖ʙ

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($ͷର৅ͱ͢Δ

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ͭ·Γࠓ ͭͷจࣈྻ͸ ͲΕ΋ڧࢀর͕ͳ͍ ($͞Εͦ͏ʂ

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͕Μ͹ͬͯ($͢Δ ($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($ͷର৅ͱ͢Δ ͕Μ͹ͬͯ($͢Δ ($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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͜Ε΋͔ͯ͠͠ʂ 4ZTUFNHD ͔ͳʁ

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Ͱ΋ 4ZTUFNHD ݺΜͰ΋ ($͞ΕΔͱ͸ݶΒͳ͍ͬͯ ͹ͬͪΌ͕ݴͬͯͨ

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͕Μ͹ͬͯ($͢Δ

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+BWBԾ૝Ϛγϯ಺ͷۭ͖ϝϞϦʔͷྔΛฦ͠·͢ɻ HDϝιουΛݺͼग़͢ͱɺ GSFF.FNPSZʹΑͬͯฦ͞ΕΔ஋͕૿͑Δ৔߹͕͋Γ·͢ɻ 3VOUJNFGSFF.FNPSZ +BWB%PDΑΓ

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͕Μ͹ͬͯ($͢Δ

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($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ ($͞Εͯͳ͍͜ͱΛ֬ೝ͢Δ ($ͷର৅ͱ͢Δ ͕Μ͹ͬͯ($͢Δ ($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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͜ͷࢀরΦϒδΣΫτ͕ɺ ϓϩάϥϜ·ͨ͸ΨϕʔδɾίϨΫλʹΑͬͯ ΩϡʔʹೖΕΒΕ͍ͯΔ͔Ͳ͏͔Λ൑ఆ͠·͢ɻ 3FGFSFODFJT&ORVFVFE +BWB%PDΑΓ

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ͭ·Γ ऑࢀর ($ͷର৅ͱͳΔ ΠϯελϯεΛ ΨϕʔδίϨΫλ͞Μ͕ݟ͚ͭΔͱ ݪࢠతʹΫϦΞ͢Δʁ($͕ى͖Δ

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ͭ·Γ ͦͷΫϦΞ ($ ର৅ʹͳͬͨऑࢀর͕ ΩϡʔʹೖΔʁ

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ͭ·Γ Ωϡʔʹೖ͍ͬͯΕ͹ ($͞ΕͨͱΈͳͯ͠0,ʁʁʁ

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($͞ΕͯΔ͔Ͳ͏͔֬ೝ͢Δ

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ͳ Δ ΄ Ͳ

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Ϧςϥϧ($͞Εͯͳ͍Α OFXͨ͠΍ͭ($͞ΕͨΑ‷ ɾŷɾ و ̑̑ŞƄŕ JOUFSOͨ͠΍ͭ($͞ΕͨΑ‷ ɾŷɾ و ̑̑ŞƄŕ ݁Ռ

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݁Ռ Ϧςϥϧ͸($ͷର৅֎ʂ 4USJOHͷΠϯελϯε ώʔϓ্ʹ͋Δ΋ͷʁ ͸ ଞͷΠϯελϯεͱಉ༷($ର৅͚ͩͲ 4USJOHϓʔϧ͸ର৅֎ʂ

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͠ΐʔ΋ͳ͍ͭͿ΍͖͕ɾɾɾ

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ײ૝ ίʔυॻ͍͙ͯ֬͢ೝͰ͖Δͷ͍͢͝ʂ ౰࣌ΫιΈ͍ͨͳπΠʔτͨͭ͠΋Γ͚ͩͬͨͲ Ԟ͕ਂ͔ͬͨʂ ଞਓͷ᧓Ͱ૬๾ΛͱͬͨΈ͍ͨͳ࿩ʹͳ͚ͬͨͲ ͜ΕΛࣗ෼Ͱग़དྷΔΑ͏ʹͳΒͳ͍ͱͳΜͩʂ