8 pictures to understand Java

A picture is worth a thousand words, and the following diagrams are from the Java tutorials on Program Creek, which currently have the most votes. If the diagram doesn't explain the problem, then you can use its title to get a glimpse of it.

1. String immutability

The following image shows what this code does.

 String s = "abcd" ;
 s = s.concat( "ef" );

2. The difference between the equals() method and the hashCode() method

HashCode is designed to improve performance. The difference between the equals() method and the hashCode() method is:

1. If two objects are equal, then they must have the same hash value.
2. If two objects have the same hash value, they are not necessarily equal.

3. Hierarchy of Java exception classes

The red parts in the figure are checked exceptions. They must be caught or declared as thrown in the function.

4. Hierarchy of collection classes

Note the difference between Collections and Collection. (Collections contain various static polymorphic methods related to collection operations)

#p#

5. Java synchronization

Java synchronization mechanism can be explained by the analogy of a building.

6. Aliases

Aliases mean that there are multiple variables pointing to the same memory block that can be updated, and these aliases are different object types.

7. Heap and Stack

The diagram shows where methods and objects are located in memory at runtime.

8. Java virtual machine runtime data area

The diagram shows the entire virtual machine runtime data area.

Original link: programcreek
Translation link: http://www.importnew.com/11725.html