$ java StringLayout (JDK 27) java.version = 27 vm.flags = -XX:+EnableDynamicAgentLoading # WARNING: Unable to attach Serviceability Agent. sun.jvm.hotspot.runtime.VM.isCompressedKlassPointersEnabled() # Field sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 # Array element sizes: 4, 1, 1, 2, 2, 4, 4, 8, 8 === java.lang.String, the class java.lang.String object internals: OFF SZ TYPE DESCRIPTION VALUE 0 8 (object header: mark) N/A 8 4 int String.hash N/A 12 1 byte String.coder N/A 13 1 boolean String.hashIsZero N/A 14 2 (alignment/padding gap) 16 4 byte[] String.value N/A 20 4 (object alignment gap) Instance size: 24 bytes Space losses: 2 bytes internal + 4 bytes external = 6 bytes total === one Latin-1 string and one UTF-16 string, field by field java.lang.String object internals: OFF SZ TYPE DESCRIPTION VALUE 0 8 (object header: mark) 0x0017cc0000000001 (Lilliput) 8 4 int String.hash 0 12 1 byte String.coder 0 13 1 boolean String.hashIsZero false 14 2 (alignment/padding gap) 16 4 byte[] String.value [104, 101, 108, 108, 111] 20 4 (object alignment gap) Instance size: 24 bytes Space losses: 2 bytes internal + 4 bytes external = 6 bytes total java.lang.String object internals: OFF SZ TYPE DESCRIPTION VALUE 0 8 (object header: mark) 0x0017cc0000000001 (Lilliput) 8 4 int String.hash 0 12 1 byte String.coder 1 13 1 boolean String.hashIsZero false 14 2 (alignment/padding gap) 16 4 byte[] String.value [104, 0, -84, 32, 108, 0, 108, 0, 111, 0] 20 4 (object alignment gap) Instance size: 24 bytes Space losses: 2 bytes internal + 4 bytes external = 6 bytes total === the byte[] behind each [B object internals: OFF SZ TYPE DESCRIPTION VALUE 0 8 (object header: mark) 0x0017980000000001 (Lilliput) 8 4 (array length) 5 12 5 byte [B. N/A 17 7 (object alignment gap) Instance size: 24 bytes Space losses: 0 bytes internal + 7 bytes external = 7 bytes total [B object internals: OFF SZ TYPE DESCRIPTION VALUE 0 8 (object header: mark) 0x0017980000000001 (Lilliput) 8 4 (array length) 10 12 10 byte [B. N/A 22 2 (object alignment gap) Instance size: 24 bytes Space losses: 0 bytes internal + 2 bytes external = 2 bytes total === footprint by length (String object + its byte[], via GraphLayout) chars content coder byte[].length String byte[] total 0 ASCII 0 0 24 16 40 0 U+00E9 0 0 24 16 40 0 U+20AC 0 0 24 16 40 1 ASCII 0 1 24 16 40 1 U+00E9 0 1 24 16 40 1 U+20AC 1 2 24 16 40 5 ASCII 0 5 24 24 48 5 U+00E9 0 5 24 24 48 5 U+20AC 1 10 24 24 48 10 ASCII 0 10 24 24 48 10 U+00E9 0 10 24 24 48 10 U+20AC 1 20 24 32 56 20 ASCII 0 20 24 32 56 20 U+00E9 0 20 24 32 56 20 U+20AC 1 40 24 56 80 40 ASCII 0 40 24 56 80 40 U+00E9 0 40 24 56 80 40 U+20AC 1 80 24 96 120 100 ASCII 0 100 24 112 136 100 U+00E9 0 100 24 112 136 100 U+20AC 1 200 24 216 240 1000 ASCII 0 1000 24 1016 1040 1000 U+00E9 0 1000 24 1016 1040 1000 U+20AC 1 2000 24 2016 2040