1.java.io Provides for system input and output through data streams, serialization and the file system.2.java.lang Provides classes that are fundamental to the design of the Java programming language.3.java.sql Provides the API for accessing and processing data stored in a data source (usually a relational database) using the JavaTM programming language.4.java.util Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array). ........ Java API
Provides for system input and output through data streams, serialization and the file system.2.java.lang
Provides classes that are fundamental to the design of the Java programming language.3.java.sql
Provides the API for accessing and processing data stored in a data source (usually a relational database) using the JavaTM programming language.4.java.util
Contains the collections framework, legacy collection classes, event model, date and time facilities, internationalization, and miscellaneous utility classes (a string tokenizer, a random-number generator, and a bit array).
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Java API
java.util 实用工具类
java.io 标准输入输出
java.net 网络功能类库
java.awt 组件标准GUI
java.applet 提供对applet的支持
可以在书上或是文档里面找到。我这里有文档。如果需要可以给你发一份!希望对你有帮助!!