When you create an instance of a class with the new keyword, all constructors in the constructor chain are automatically called. But if an object implements the Cloneable interface, we can call its clone() method. The clone() method does not call any class constructors.
When using the Design Pattern, if you create an object in Factory mode, it is very simple to create a new object instance using the clone() method. For example, the following is a typical implementation of the Factory pattern:
Public staTIc Credit getNewCredit() {
Return new Credit();
}
The improved code uses the clone() method as follows:
Private staTIc Credit BaseCredit = new Credit();
Public staTIc Credit getNewCredit() {
Return (Credit) BaseCredit.clone();
}
The above ideas are also useful for array processing.
1.2 Using non-blocking I/OThe lower version of the JDK does not support non-blocking I/O APIs. To avoid I/O blocking, some applications use a way to create a large number of threads (in a better case, a buffer pool is used). This technology can be seen in many applications that must support concurrent I/O streams, such as web servers, quotations, and auction applications. However, creating Java threads requires considerable overhead.
JDK 1.4 introduces a non-blocking I/O library (java.nio). If your application requires an older version of the JDK, there is a package that supports non-blocking I/O.
See "Adjusting Java I/O Performance" on the Sun China website.
1.3 Use exceptions with cautionAnomalies are detrimental to performance. To throw an exception, you first need to create a new object. The constructor of the Throwable interface calls the local (NaTIve) method called fillInStackTrace(), which checks the stack and collects call trace information. As long as an exception is thrown, the VM must adjust the call stack because a new object is created during processing.
Exceptions can only be used for error handling and should not be used to control program flow.
1.4 Do not repeat initialization variablesBy default, when the class's constructor is called, Java initializes the variable to a definite value: all objects are set to null, integer variables (byte, short, int, long) are set to 0, and float and double variables are set to 0.0, the logical value is set to false. This should be especially noted when a class is derived from another class, because when an object is created with the new keyword, all constructors in the constructor chain are automatically called.
1.5 Try to specify the final modifier of the classClasses with the final modifier are not derivable. In the Java core API, there are many examples of final applications, such as java.lang.String. Specifying a final for the String class prevents people from overriding the length() method.
In addition, if you specify a class as final, all methods of the class are final. The Java compiler will look for opportunities to inline all the final methods (this is related to the specific compiler implementation). This can increase performance by an average of 50%.
1.6 Try to use local variablesThe parameters passed when the method is called and the temporary variables created in the call are saved on the stack, which is faster. Other variables, such as static variables, instance variables, etc., are created in the heap (Heap), which is slower. In addition, depending on the specific compiler/JVM, local variables may be further optimized. See "Using Stack Variables Whenever possible."
1.7 Multiplication and divisionConsider the following code:
For (val = 0; val < 100000; val +=5) { alterX = val * 8; myResult = val * 2; }
Substituting shift operations for multiply operations can greatly improve performance. Here is the modified code:
For (val = 0; val < 100000; val += 5) { alterX = val << 3; myResult = val << 1; }
The modified code no longer does the multiplication by 8, but instead uses the equivalent left shift 3-bit operation, and shifting 1 bit to the left is equivalent to multiplying by 2. Accordingly, shifting the right bit by one operation is equivalent to dividing by two. It is worth mentioning that although the shift operation is fast, it may make the code more difficult to understand, so it is best to add some comments.
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