Code optimization tips in Java

As a popular and widely used programming language, Java's code optimization skills are also one of the focuses of developers. This article will introduce some commonly used Java code optimization techniques to help improve program performance.

1. Use StringBuilder instead of String for string splicing

In Java, since String is immutable, a new String object will be created every time string splicing is performed. Can reduce program performance when doing heavy string processing. Therefore, we can use StringBuilder, a variable string class, to replace String for string concatenation, thereby improving program performance.

The sample code is as follows:

String str = "";
for(int i=0; i<1000; i++){
    str += i;
}

can be replaced by:

StringBuilder sb = new StringBuilder();
for(int i=0; i<1000; i++){
    sb.append(i);
}
String str = sb.toString();

2. Specify the initial capacity when using the collection class

For ArrayList, For collection classes such as HashMap, it is best to specify the initial capacity when using them, so that frequent expansion operations can be avoided to a certain extent. Especially when the number of elements stored in the collection is large, the effect of this optimization will be more obvious.

The sample code is as follows:

List<Integer> list = new ArrayList<>();
// 进行大量操作
list.add(1);
list.add(2);
list.add(3);

can be replaced by:

List<Integer> list = new ArrayList<>(1000);
// 进行大量操作
list.add(1);
list.add(2);
list.add(3);

3. Use try-catch-finally instead of try-with-resources

In Java 7, the try-with-resources syntax was introduced to automatically close resources. However, in some cases, using try-catch-finally is more efficient.

When using try-with-resources, the JVM will create a try-finally block for each resource. Therefore, this may cause a stack overflow if a large amount of resources needs to be processed.

The sample code is as follows:

try(InputStream in = new FileInputStream("file.txt")){
    // 处理文件流
} catch(IOException e) {
    // 异常处理
}

can be replaced with:

InputStream in = null;
try{
    in = new FileInputStream("file.txt");
    // 处理文件流
} catch(IOException e) {
    // 异常处理
} finally {
    if (in != null) {
        try {
            in.close();
        } catch (IOException e) {
            // 异常处理
        }
    }
}

4. Use static final constants instead of hard-coded values

hard Encoded values ​​can lead to problems such as poor readability, poor maintainability, and duplicate code. Using static final constants can avoid these problems and improve the efficiency of the program.

The sample code is as follows:

public static double calculateArea(double radius) {
    double pi = 3.14159265358979323846;
    return pi * radius * radius;
}

can be replaced by:

public static final double PI = 3.14159265358979323846;
public static double calculateArea(double radius) {
    return PI * radius * radius;
}

5. Use local variables instead of member variables

In Java, Member variables can be accessed by multiple methods, thus increasing the size and overhead of the object instance. Using local variables can avoid these problems and improve the efficiency of the program.

The sample code is as follows:

public class Test {
    private int num;

    public void setNum(int num) {
        this.num = num;
    }

    public void doSomething() {
        for (int i = 0; i < 1000; i++) {
            // 使用 num
        }
    }
}

can be replaced by:

public class Test {
    public void setNum(int num) {
        // do something
    }

    public void doSomething() {
        int num = 0;
        for (int i = 0; i < 1000; i++) {
            // 使用 num
        }
    }
}

The above are some commonly used Java code optimization techniques. Of course, code optimization is not static and needs to be optimized according to specific circumstances in order to maximize program performance.

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