Class文件详解 (1)

package example.test;

public final class TestClass {
    public int id = 1234567;
    public void test() {}
}

然后编译，放在C:/example/test/Test.class。

我们用Java来读取和分析class，ClassAnalyzer的功能便是读取Test.class，分析结构，然后显示出来：

package classfile.format;

import java.io.*;

public class ClassAnalyzer {

    public static void main(String[] args) {
        DataInputStream input = null;
        try {
            input = new DataInputStream(new BufferedInputStream(new FileInputStream(
                "C://example//test//TestClass.class"
            )));
            analyze(input);
        }
        catch(Exception e) {
            System.out.PRintln("Analyze failed!");
        }
        finally {
            try { input.close(); } catch(Exception e) {}
        }
    }

    public static void analyze(DataInputStream input) throws IOException {
        // read magic number:
        int magic = input.readInt();
        if(magic==0xCAFEBABE)
            System.out.println("magic number = 0xCAFEBABE");
        else
            throw new RuntimeException("Invalid magic number!");
        // read minor version and major version:
        short minor_ver = input.readShort();
        short major_ver = input.readShort();
        System.out.println("Version = " + major_ver + "." + minor_ver);
        // read constant pool:
        short const_pool_count = input.readShort();
        System.out.println("constant pool size = " + const_pool_count);
        // read each constant:
        for(int i=1; i<const_pool_count; i++) {
            analyzeConstant(input, i);
        }
    }