Put this line into class main method: String a = “i042416”; And decompile the .class file using javap:
We can see the “i042416” is included in the constant pool:
The java code String a = “i042416” is implemented via two lines of codes below:
(1) When the class is loaded by JVM, the string “i042416” is represented by #16. When instruction ldc #16 is called for the first time, the native method StringTable::intern will be called to generate char[], and store the reference into StringTable and constant pool. When the ldc #16 is called subsequently, the reference #16 is directly returned from constant pool.
(2) Instruction astore_1 stores the reference of “i042416” to local variable table. Test via these lines instead: String aa1 = “i042416”; String aa2 = “jerrywang”; String aa3 = “i042416” + “jerrywang”; We can see for line aa3, the string concatenation is done in compilation time.
As a result, the following println gets true as result: String aa1 = “i042416jerrywang”; String aa2 = “jerrywang”; String aa3 = “i042416” + “jerrywang”; System.out.println(aa1 == aa3);
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汪子熙 认证博客专家 前端框架 Node.js SAP JerryWang，2007年从电子科技大学计算机专业硕士毕业后加入SAP成都研究院工作至今。Jerry是SAP社区导师，SAP中国技术大使。2020年5月下旬，Jerry做了脑部肿瘤的开颅切除手术，对编程和人生又有了新的感悟。