Class文件詳解 (2)

2019-11-18 14:53:39

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　　今天繼續(xù)分析Class文件的結(jié)構(gòu)。

上次讀取了constant pool，緊接著是這個(gè)類或接口的 access flags，JVM定義的關(guān)于class或interface的Access flags有：

    PRivate static short ACC_PUBLIC    = 0x0001;
    private static short ACC_FINAL     = 0x0010;
    private static short ACC_SUPER     = 0x0020;
    private static short ACC_INTERFACE = 0x0200;
    private static short ACC_ABSTRACT = 0x0400;

    // read access flags:
    short access_flags = input.readShort();
    System.out.print("Access flags:");
    if((access_flags & ACC_PUBLIC) == ACC_PUBLIC)
        System.out.print(" public");
    if((access_flags & ACC_FINAL) == ACC_FINAL)
        System.out.print(" final");
    if((access_flags & ACC_SUPER) == ACC_SUPER)
        System.out.print(" super");
    if((access_flags & ACC_INTERFACE) == ACC_INTERFACE)
        System.out.print(" interface");
    if((access_flags & ACC_ABSTRACT) == ACC_ABSTRACT)
        System.out.print(" abstract");
    System.out.println();

然后是this class和super class：

    // read this class and super class:
    short this_class_index = input.readShort();
    short super_class_index = input.readShort();
    System.out.println("This class = " + this_class_index);
    System.out.println("Super class = " + super_class_index);

根據(jù)this class的index可以從constant pool中得到這個(gè)class的信息，super class也一樣。每個(gè)class都有super class，只有Object的super class index=0。

接下來(lái)是這個(gè)class繼續(xù)了多少個(gè)interface和每個(gè)interface在constant pool中的index：

    // read interfaces count:
    short interfaces_count = input.readShort();
    System.out.println("Interfaces count = " + interfaces_count);
    // read each interface:
    for(int i=1; i<=interfaces_count; i++) {
        short interface_index = input.readShort();
        System.out.println("No. " + i + " interface index = " + interface_index);
    }

結(jié)果如下：

    Access flags: public final super
    This class = 2
    Super class = 4
    Interfaces count = 0

待續(xù)...

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