Detailed explanation of using javap to analyze Java string operations

This article brings you a detailed explanation of using javap to analyze Java string operations. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

Let’s look at this line of Java code for a simple string assignment operation.

String a = "i042416";

Use the command line to decompile the Java class containing this line of code to view its bytecode:

javap -v constant.ConstantFolding

We see that the string "i042416" was added to the constant pool by the Java compiler.

##Java code String a = "i042416" is translated into the following two sentences of bytecode:

ldc #16: First, the underlying native method of JVM, StringTable::intern, is called to generate the internal storage implementation of String, char[]. Then execute ldc #16 to load the constant code-named #16 in the constant pool onto the stack, i.e. i042416.

2. astore_1: Store the reference of "i042416" into the local variable with serial number 1 (that is, local variable a in our code).

Let’s look at a slightly more complex example.

Do a string splicing operation.

String aa1 = "i042416";
String aa2 = "jerrywang";
String aa3 = "i042416" + "jerrywang";

You can see that during the compilation phase, the compiler byte splices the values ​​​​of the two string constants, and the result "i042416jerrywang" is stored in the variable aa3, as a new string constant, in the constant The codename in the pool is #21.

## Therefore, the variables aa1 and aa3 actually point to the constant pool The same constant in , so direct comparison with == will also return true.

String aa1 = "i042416jerrywang";
String aa2 = "jerrywang";
String aa3 = "i042416" + "jerrywang";
System.out.println(aa1 == aa3);

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