strings: Java Strings deep dive companion code (pool/intern, indy concat vs StringBuilder JMH, text blocks, string templates)
Co-Authored-By: Claude Sonnet 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01KqJyCidz3ZgRyHABv2GVJh
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Claude
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literal == literal : true
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literal == new String : false
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literal.equals(new String) : true
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literal == c.intern() : true
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constant + literal == "hello" : true
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runtime concat == "hello" : false
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runtime concat.intern() == "hello": true
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built "java".intern() == the built instance : false
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built unseen string .intern() == the built instance: true
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--- closing delimiter on its own line, aligned with the text ---
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{\n
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.."id":.1\n
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}\n
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--- closing delimiter right after the last line (no final newline) ---
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{\n
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.."id":.1\n
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}
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--- closing delimiter 2 columns left of the text: 2 spaces of indentation survive ---
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..left\n
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--- trailing spaces are stripped, but \s and \040 survive ---
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x....\n
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y.\n
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--- backslash at end of line joins the lines ---
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one.line\n
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--- escapes are processed after indentation is stripped ---
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tab: |\n
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--- double quotes need no escape; only a run of three does ---
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say."hi".and."""\n
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two identical text blocks are the same pooled instance: true
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equals the hand-written literal: true
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--- formatted() is the built-in way to interpolate ---
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Hello,.Ann!.You.are.30.\n
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iteration 0: length=1 value=0
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iteration 1: length=2 value=01
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iteration 2: length=3 value=012
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iteration 3: length=4 value=0123
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iteration 4: length=5 value=01234
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characters copied in total across the loop results: 15
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n=20000: final length=20000, characters in all intermediate strings=200010000
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$ javac ConcatShapes.java && javap -c -p ConcatShapes (method one)
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public static java.lang.String one(java.lang.String, int);
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Code:
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0: aload_0
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1: iload_1
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2: invokedynamic #7, 0 // InvokeDynamic #0:makeConcatWithConstants:(Ljava/lang/String;I)Ljava/lang/String;
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7: areturn
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$ javac -XDstringConcat=inline ConcatShapes.java && javap -c -p ConcatShapes (method one)
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public static java.lang.String one(java.lang.String, int);
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Code:
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0: new #7 // class java/lang/StringBuilder
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3: dup
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4: invokespecial #9 // Method java/lang/StringBuilder."<init>":()V
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7: ldc #10 // String user=
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9: invokevirtual #12 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
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12: aload_0
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13: invokevirtual #12 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
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16: ldc #16 // String n=
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18: invokevirtual #12 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
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21: iload_1
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22: invokevirtual #18 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
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25: invokevirtual #21 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
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28: areturn
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$ javap -c -v ConcatShapes | grep -A3 BootstrapMethods
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BootstrapMethods:
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0: #39 REF_invokeStatic java/lang/invoke/StringConcatFactory.makeConcatWithConstants:(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/invoke/CallSite;
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Method arguments:
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#37 user=\u0001 n=\u0001
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InnerClasses:
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$ javac StringTemplate.java
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src/broken/StringTemplate.java:4: error: illegal escape character
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System.out.println(STR."Hello, \{name}");
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^
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1 error
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$ javac --enable-preview --release 25 StringTemplate.java
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src/broken/StringTemplate.java:4: error: illegal escape character
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System.out.println(STR."Hello, \{name}");
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^
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1 error
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bool CompactStrings = true {pd product} {default}
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bool OptimizeStringConcat = true {C2 product} {default}
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uintx StringTableSize = 65536 {product} {default}
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bool UseStringDeduplication = false {product} {default}
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Benchmark (loop) Mode Cnt Score Error Units
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ConcatBenchmark.explicitBuilder N/A avgt 10 20.838 ± 2.629 ns/op
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ConcatBenchmark.formattedMethod N/A avgt 10 164.278 ± 12.164 ns/op
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ConcatBenchmark.plusExpression N/A avgt 10 20.448 ± 7.264 ns/op
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ConcatBenchmark.plusLatin1 N/A avgt 10 15.791 ± 4.953 ns/op
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ConcatBenchmark.plusUtf16 N/A avgt 10 23.185 ± 4.275 ns/op
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ConcatBenchmark.stringFormat N/A avgt 10 285.885 ± 133.980 ns/op
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LoopConcatBenchmark.loopBuilder 100 avgt 5 270.251 ± 128.322 ns/op
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LoopConcatBenchmark.loopBuilder 1000 avgt 5 2268.140 ± 888.134 ns/op
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LoopConcatBenchmark.loopBuilder 10000 avgt 5 24468.200 ± 8712.080 ns/op
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LoopConcatBenchmark.loopBuilderPresized 100 avgt 5 194.101 ± 168.069 ns/op
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LoopConcatBenchmark.loopBuilderPresized 1000 avgt 5 1682.224 ± 135.261 ns/op
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LoopConcatBenchmark.loopBuilderPresized 10000 avgt 5 20622.063 ± 16702.078 ns/op
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LoopConcatBenchmark.loopPlusEquals 100 avgt 5 2021.521 ± 648.577 ns/op
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LoopConcatBenchmark.loopPlusEquals 1000 avgt 5 73764.547 ± 11968.016 ns/op
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LoopConcatBenchmark.loopPlusEquals 10000 avgt 5 8939940.357 ± 2388632.875 ns/op
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-------------------------------------------------------------------------------
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Test set: com.ankurm.strings.StringBehaviourTest
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-------------------------------------------------------------------------------
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Tests run: 8, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.252 s -- in com.ankurm.strings.StringBehaviourTest
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