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These reference types also have methods for extracting the primitive type from them. The version of the class file created by the Java compiler of Java SE 7 is 51.0. Therefore, class files with version 51.0 cannot be executed in the Java SE 6 JVM. But the Java Bytecode is written in a language that a human can understand, rather than in the language that the machine directly executes. Therefore, the execution engine must change the bytecode to the language that can be executed by the machine in the JVM. The bytecode can be changed to the suitable language in one of two ways.

You’ve already learned about looping in previous sections. Well, array lists have a forEach() method of their own that takes a lambda expression as parameter and can perform an action on all the elements of the array list. All you have to do is replace the primitive data type with the equivalent wrapper class.

Java Methods

A significantly longer bytecode than the Java source code has been created. First, you can see that lookupswitch instruction has been used for switch() statement in Java bytecode. However, two lookupswitch instructions have been used, not the one lookupswitch instruction. When disassembling the case in which int has been added to switch() statement, only one lookupswitch instruction has been used. This means that the switch() statement has been divided into two statements to process the string.

• Since abc was already in the string pool, the literalString2 variable reuses that.
• The first 16 bytes of the UserService.class file disassembled earlier are shown as follows in the Hex Editor.
• Hash maps in Java can store elements in key-value pairs.
• If you didn’t understand every aspect of this section word by word, don’t worry.
• However, if you understand JVM, you will understand Java more, and it will be helpful to solve the problems like the case we have reviewed here.

But when you add the (int) cast operator explicitly, you show the compiler who’s boss. Type conversion in Java can be either “implicit” or “explicit”. Java 7 SE Lessons When the compiler converts a smaller type of data to a larger one automatically, it’s known as an implicit or narrowing type conversion.

Runtime Data Areas

You can also compare multidimensional arrays, but for that you’ll have to use the Arrays.deepEquals() method instead of the regular one. In cases where the given item is not found, you’ll get a negative index. The resultant negative index will vary based on a number of factors but I won’t get into those here. If you’re interested in learning more, check out my article on the topic.