用Java实现JVM第三章《解析class文件》

落日映苍穹つ 2023-01-06 05:48 96阅读 0赞

## 案例介绍 ##

本案例主要介绍通过java代码从class文件中解析；class文件、常量池、属性表；

> 作为类（或者接口）信息的载体，每个class文件都完整地定义了一个类。为了使java程序可以“编写一次，处处运行”，Java虚拟机规范对class文件格式进行了严格的规定。但是另外一方面，对于从哪里加载class文件，给了足够多的自由。Java虚拟机实现可以从文件系统读取和从JAR（或ZIP）压缩包中提取clss文件。除此之外，也可以通过网络下载、从数据库加载，甚至是在运行中直接生成class文件。Java虚拟机规范中所指的class文件，并非特指位于磁盘中的.class文件，而是泛指任何格式符号规范的class数据。

## 环境准备 ##

jdk 1.8.0  
IntelliJ IDEA Community Edition 2018.3.1 x64

## 配置信息 ##

调试配置  
配置位置：Run/Debug Configurations -> program arguments  
配置内容：-Xjre “C:\\Program Files\\Java\\jdk1.8.0\_161\\jre” java.lang.String

## 代码示例 ##

itstack-demo-jvm-03
    ├── pom.xml
    └── src
        └── main
        │    └── java
        │        └── org.itstack.demo.jvm
    	│             ├── classfile
        │             │   ├── attributes   {BootstrapMethods/Code/ConstantValue...}
        │             │   ├── constantpool {CONSTANT_TAG_CLASS/CONSTANT_TAG_FIELDREF/CONSTANT_TAG_METHODREF...}
        │             │   ├── ClassFile.java
        │             │   ├── ClassReader.java
        │             │   └── MemberInfo.java	
        │             ├── classpath
        │             │   ├── impl
        │             │   │   ├── CompositeEntry.java
        │             │   │   ├── DirEntry.java 
        │             │   │   ├── WildcardEntry.java 
        │             │   │   └── ZipEntry.java    
        │             │   ├── Classpath.java
        │             │   └── Entry.java    
        │             ├── Cmd.java
        │             └── Main.java
        └── test
             └── java
                 └── org.itstack.demo.test
                     └── HelloWorld.java

代码篇幅较长，不一一列举。

AttributeInfo.java

package org.itstack.demo.jvm.classfile.attributes;
    
    import org.itstack.demo.jvm.classfile.ClassReader;
    import org.itstack.demo.jvm.classfile.attributes.impl.*;
    import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/4/26
     */
    public interface AttributeInfo {
    
        void readInfo(ClassReader reader);
    
        static AttributeInfo[] readAttributes(ClassReader reader, ConstantPool constantPool) {
            int attributesCount = reader.readU2ToInt();
            AttributeInfo[] attributes = new AttributeInfo[attributesCount];
            for (int i = 0; i < attributesCount; i++) {
                attributes[i] = readAttribute(reader, constantPool);
            }
            return attributes;
        }
    
        static AttributeInfo readAttribute(ClassReader reader, ConstantPool constantPool) {
            int attrNameIdx = reader.readU2ToInt();
            String attrName = constantPool.getUTF8(attrNameIdx);
            int attrLen = reader.readU4ToInt();
            AttributeInfo attrInfo = newAttributeInfo(attrName, attrLen, constantPool);
            attrInfo.readInfo(reader);
            return attrInfo;
        }
    
        static AttributeInfo newAttributeInfo(String attrName, int attrLen, ConstantPool constantPool) {
            switch (attrName) {
                case "BootstrapMethods":
                    return new BootstrapMethodsAttribute();
                case "Code":
                    return new CodeAttribute(constantPool);
                case "ConstantValue":
                    return new ConstantValueAttribute();
                case "Deprecated":
                    return new DeprecatedAttribute();
                case "EnclosingMethod":
                    return new EnclosingMethodAttribute(constantPool);
                case "Exceptions":
                    return new ExceptionsAttribute();
                case "InnerClasses":
                    return new InnerClassesAttribute();
                case "LineNumberTable":
                    return new LineNumberTableAttribute();
                case "LocalVariableTable":
                    return new LocalVariableTableAttribute();
                case "LocalVariableTypeTable":
                    return new LocalVariableTypeTableAttribute();
                // case "MethodParameters":
                // case "RuntimeInvisibleAnnotations":
                // case "RuntimeInvisibleParameterAnnotations":
                // case "RuntimeInvisibleTypeAnnotations":
                // case "RuntimeVisibleAnnotations":
                // case "RuntimeVisibleParameterAnnotations":
                // case "RuntimeVisibleTypeAnnotations":
                case "Signature":
                    return new SignatureAttribute(constantPool);
                case "SourceFile":
                    return new SourceFileAttribute(constantPool);
                // case "SourceDebugExtension":
                // case "StackMapTable":
                case "Synthetic":
                    return new SyntheticAttribute();
                default:
                    return new UnparsedAttribute(attrName, attrLen);
            }
    
        }
    
    }

ConstantInfo.java

package org.itstack.demo.jvm.classfile.constantpool;
    
    import org.itstack.demo.jvm.classfile.ClassReader;
    import org.itstack.demo.jvm.classfile.constantpool.impl.*;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/4/26
     */
    public interface ConstantInfo {
    
        int CONSTANT_TAG_CLASS = 7;
        int CONSTANT_TAG_FIELDREF = 9;
        int CONSTANT_TAG_METHODREF = 10;
        int CONSTANT_TAG_INTERFACEMETHODREF = 11;
        int CONSTANT_TAG_STRING = 8;
        int CONSTANT_TAG_INTEGER = 3;
        int CONSTANT_TAG_FLOAT = 4;
        int CONSTANT_TAG_LONG = 5;
        int CONSTANT_TAG_DOUBLE = 6;
        int CONSTANT_TAG_NAMEANDTYPE = 12;
        int CONSTANT_TAG_UTF8 = 1;
        int CONSTANT_TAG_METHODHANDLE = 15;
        int CONSTANT_TAG_METHODTYPE = 16;
        int CONSTANT_TAG_INVOKEDYNAMIC = 18;
    
        void readInfo(ClassReader reader);
    
        int tag();
        
        static ConstantInfo readConstantInfo(ClassReader reader, ConstantPool constantPool) {
            int tag = reader.readU1ToInt();
            ConstantInfo constantInfo = newConstantInfo(tag, constantPool);
            constantInfo.readInfo(reader);
            return constantInfo;
        }
    
        static ConstantInfo newConstantInfo(int tag, ConstantPool constantPool) {
            switch (tag) {
                case CONSTANT_TAG_INTEGER:
                    return new ConstantIntegerInfo();
                case CONSTANT_TAG_FLOAT:
                    return new ConstantFloatInfo();
                case CONSTANT_TAG_LONG:
                    return new ConstantLongInfo();
                case CONSTANT_TAG_DOUBLE:
                    return new ConstantDoubleInfo();
                case CONSTANT_TAG_UTF8:
                    return new ConstantUtf8Info();
                case CONSTANT_TAG_STRING:
                    return new ConstantStringInfo(constantPool);
                case CONSTANT_TAG_CLASS:
                    return new ConstantClassInfo(constantPool);
                case CONSTANT_TAG_FIELDREF:
                    return new ConstantFieldRefInfo(constantPool);
                case CONSTANT_TAG_METHODREF:
                    return new ConstantMethodRefInfo(constantPool);
                case CONSTANT_TAG_INTERFACEMETHODREF:
                    return new ConstantInterfaceMethodRefInfo(constantPool);
                case CONSTANT_TAG_NAMEANDTYPE:
                    return new ConstantNameAndTypeInfo();
                case CONSTANT_TAG_METHODTYPE:
                    return new ConstantMethodTypeInfo();
                case CONSTANT_TAG_METHODHANDLE:
                    return new ConstantMethodHandleInfo();
                case CONSTANT_TAG_INVOKEDYNAMIC:
                    return new ConstantInvokeDynamicInfo();
                default:
                    throw new ClassFormatError("constant pool tag");
            }
        }
    }

ClassFile.java

package org.itstack.demo.jvm.classfile;
    
    import org.itstack.demo.jvm.classfile.attributes.AttributeInfo;
    import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/4/26
     */
    public class ClassFile {
    
        private int minorVersion;
        private int majorVersion;
        private ConstantPool constantPool;
        private int accessFlags;
        private int thisClassIdx;
        private int supperClassIdx;
        private int[] interfaces;
        private MemberInfo[] fields;
        private MemberInfo[] methods;
        private AttributeInfo[] attributes;
    
        public ClassFile(byte[] classData) {
            ClassReader reader = new ClassReader(classData);
            this.readAndCheckMagic(reader);
            this.readAndCheckVersion(reader);
            this.constantPool = this.readConstantPool(reader);
            this.accessFlags = reader.readU2ToInt();
            this.thisClassIdx = reader.readU2ToInt();
            this.supperClassIdx = reader.readU2ToInt();
            this.interfaces = reader.readUInt16s();
            this.fields = MemberInfo.readMembers(reader, constantPool);
            this.methods = MemberInfo.readMembers(reader, constantPool);
            this.attributes = AttributeInfo.readAttributes(reader, constantPool);
        }
    
        private void readAndCheckMagic(ClassReader reader) {
            String magic = reader.readU4ToHexStr();
            if (!"cafebabe".equals(magic)) {
                throw new ClassFormatError("magic!");
            }
        }
    
        private void readAndCheckVersion(ClassReader reader) {
            this.minorVersion = reader.readU2ToInt();
            this.majorVersion = reader.readU2ToInt();
            switch (this.majorVersion) {
                case 45:
                    return;
                case 46:
                case 47:
                case 48:
                case 49:
                case 50:
                case 51:
                case 52:
                    if (this.minorVersion == 0)
                        return;
            }
            throw new UnsupportedClassVersionError();
        }
    
        private ConstantPool readConstantPool(ClassReader reader) {
            return new ConstantPool(reader);
        }
    
        public int minorVersion(){
            return this.minorVersion;
        }
    
        public int majorVersion(){
            return this.majorVersion;
        }
    
        public ConstantPool constantPool(){
            return this.constantPool;
        }
    
        public int accessFlags() {
            return this.accessFlags;
        }
    
        public MemberInfo[] fields() {
            return this.fields;
        }
    
        public MemberInfo[] methods() {
            return this.methods;
        }
    
        public String className() {
            return this.constantPool.getClassName(this.thisClassIdx);
        }
    
        public String superClassName() {
            if (this.supperClassIdx <= 0) return "";
            return this.constantPool.getClassName(this.supperClassIdx);
        }
    
        public String[] interfaceNames() {
            String[] interfaceNames = new String[this.interfaces.length];
            for (int i = 0; i < this.interfaces.length; i++) {
                interfaceNames[i] = this.constantPool.getClassName(interfaces[i]);
            }
            return interfaceNames;
        }
    
    }
    ClassReader.java
    
    package org.itstack.demo.jvm.classfile;
    
    import java.math.BigInteger;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/5/13
     * <p>
     * java虚拟机定义了u1、u2、u4三种数据类型来表示；1字节、2字节、4字节，无符号整数。
     * 在如下实现中，用增位方式表示无符号类型：
     * u1、u2可以用int类型存储，因为int类型是4字节
     * u4 需要用long类型存储，因为long类型是8字节
     */
    public class ClassReader {
    
        private byte[] data;
    
        public ClassReader(byte[] data) {
            this.data = data;
        }
    
        //u1
        public int readUint8() {
            byte[] val = readByte(1);
            return byte2int(val);
        }
    
        //u2
        public int readUint16() {
            byte[] val = readByte(2);
            return byte2int(val);
        }
    
        //u4
        public long readUint32() {
            byte[] val = readByte(4);
            String str_hex = new BigInteger(1, val).toString(16);
            return Long.parseLong(str_hex, 16);
        }
    
        public float readUint64TFloat() {
            byte[] val = readByte(8);
            return new BigInteger(1, val).floatValue();
        }
    
        public long readUint64TLong() {
            byte[] val = readByte(8);
            return new BigInteger(1, val).longValue();
        }
    
        public double readUint64TDouble() {
            byte[] val = readByte(8);
            return new BigInteger(1, val).doubleValue();
        }
    
        public int[] readUint16s() {
            int n = this.readUint16();
            int[] s = new int[n];
            for (int i = 0; i < n; i++) {
                s[i] = this.readUint16();
            }
            return s;
        }
    
        public byte[] readBytes(int n) {
            return readByte(n);
        }
    
        private byte[] readByte(int length) {
            byte[] copy = new byte[length];
            System.arraycopy(data, 0, copy, 0, length);
            System.arraycopy(data, length, data, 0, data.length - length);
            return copy;
        }
    
        private int byte2int(byte[] val) {
            String str_hex = new BigInteger(1, val).toString(16);
            return Integer.parseInt(str_hex, 16);
        }
    
    }

MemberInfo.java

package org.itstack.demo.jvm.classfile;
    
    import org.itstack.demo.jvm.classfile.attributes.AttributeInfo;
    import org.itstack.demo.jvm.classfile.attributes.impl.CodeAttribute;
    import org.itstack.demo.jvm.classfile.attributes.impl.ConstantValueAttribute;
    import org.itstack.demo.jvm.classfile.constantpool.ConstantPool;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/4/26
     */
    public class MemberInfo {
    
        private ConstantPool constantPool;
        private int accessFlags;
        private int nameIdx;
        private int descriptorIdx;
        private AttributeInfo[] attributes;
    
        public MemberInfo(ClassReader reader, ConstantPool constantPool) {
            this.constantPool = constantPool;
            this.accessFlags = reader.readU2ToInt();
            this.nameIdx = reader.readU2ToInt();
            this.descriptorIdx = reader.readU2ToInt();
            this.attributes = AttributeInfo.readAttributes(reader, constantPool);
        }
    
        public static MemberInfo[] readMembers(ClassReader reader, ConstantPool constantPool) {
            int fieldCount = reader.readU2ToInt();
            MemberInfo[] fields = new MemberInfo[fieldCount];
            for (int i = 0; i < fieldCount; i++) {
                fields[i] = new MemberInfo(reader, constantPool);
            }
            return fields;
        }
    
        public int accessFlags() {
            return this.accessFlags;
        }
    
        public String name() {
            return this.constantPool.getUTF8(this.nameIdx);
        }
    
        public String descriptor() {
            return this.constantPool.getUTF8(this.descriptorIdx);
        }
    
        public CodeAttribute codeAttribute() {
            for (AttributeInfo attrInfo : attributes) {
                if (attrInfo instanceof CodeAttribute) return (CodeAttribute) attrInfo;
            }
            return null;
        }
    
        public ConstantValueAttribute ConstantValueAttribute() {
            for (AttributeInfo attrInfo : attributes) {
                if (attrInfo instanceof ConstantValueAttribute) return (ConstantValueAttribute) attrInfo;
            }
            return null;
        }
    
    }

Main.java

package org.itstack.demo.jvm;
    
    import org.itstack.demo.jvm.classfile.ClassFile;
    import org.itstack.demo.jvm.classfile.MemberInfo;
    import org.itstack.demo.jvm.classpath.Classpath;
    
    import java.util.Arrays;
    
    /**
     * http://www.itstack.org
     * create by fuzhengwei on 2019/4/24
     */
    public class Main {
    
        public static void main(String[] args) {
            Cmd cmd = Cmd.parse(args);
            if (!cmd.ok || cmd.helpFlag) {
                System.out.println("Usage: <main class> [-options] class [args...]");
                return;
            }
            if (cmd.versionFlag) {
                //注意案例测试都是基于1.8，另外jdk1.9以后使用模块化没有rt.jar
                System.out.println("java version \"1.8.0\"");
                return;
            }
            startJVM(cmd);
        }
    
        private static void startJVM(Cmd cmd) {
            Classpath classpath = new Classpath(cmd.jre, cmd.classpath);
            System.out.printf("classpath：%s class：%s args：%s\n",
                    classpath, cmd.getMainClass(), cmd.getAppArgs());
            //获取className
            String className = cmd.getMainClass().replace(".", "/");
            ClassFile classFile = loadClass(className, classpath);
            assert classFile != null;
            printClassInfo(classFile);
        }
    
        private static ClassFile loadClass(String className, Classpath classpath) {
            try {
                byte[] classData = classpath.readClass(className);
                return new ClassFile(classData);
            } catch (Exception e) {
                System.out.println("Could not find or load main class " + className);
                return null;
            }
        }
    
        private static void printClassInfo(ClassFile cf) {
            System.out.println("version: " + cf.majorVersion() + "." + cf.minorVersion());
            System.out.println("constants count：" + cf.constantPool().getSiz());
            System.out.format("access flags：0x%x\n", cf.accessFlags());
            System.out.println("this class：" + cf.className());
            System.out.println("super class：" + cf.superClassName());
            System.out.println("interfaces：" + Arrays.toString(cf.interfaceNames()));
            System.out.println("fields count：" + cf.fields().length);
            for (MemberInfo memberInfo : cf.fields()) {
                System.out.format("  %s\n", memberInfo.name());
            }
            System.out.println("methods count: " + cf.methods().length);
            for (MemberInfo memberInfo : cf.methods()) {
                System.out.format("  %s\n", memberInfo.name());
            }
        }
    
    }

测试结果

"C:\Program Files\Java\jdk1.8.0_161\bin\java.exe" "-javaagent:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\lib\idea_rt.jar=61458:D:\Program Files\JetBrains\IntelliJ IDEA Community Edition 2018.3.1\bin" -Dfile.encoding=UTF-8 -classpath "C:\Program Files\Java\jdk1.8.0_161\jre\lib\charsets.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\deploy.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\access-bridge-64.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\cldrdata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\dnsns.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jaccess.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\jfxrt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\localedata.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\nashorn.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunec.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunjce_provider.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunmscapi.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\sunpkcs11.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\ext\zipfs.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\javaws.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jce.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfr.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jfxswt.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\jsse.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\management-agent.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\plugin.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\resources.jar;C:\Program Files\Java\jdk1.8.0_161\jre\lib\rt.jar;E:\itstack\git\istack-demo\itstack-demo-jvm\itstack-demo-jvm-03\target\classes;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\beust\jcommander\1.72\jcommander-1.72.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\org\projectlombok\lombok\1.18.0\lombok-1.18.0.jar;D:\Program Files (x86)\apache-maven-2.2.1\repository\com\alibaba\fastjson\1.2.40\fastjson-1.2.40.jar" org.itstack.demo.jvm.Main -Xjre "C:\Program Files\Java\jdk1.8.0_161\jre" java.lang.String
    classpath：org.itstack.demo.jvm.classpath.Classpath@4bf558aa class：java.lang.String args：null
    version: 52.0
    constants count：540
    access flags：0x31
    this class：java/lang/String
    super class：java/lang/Object
    interfaces：[java/io/Serializable, java/lang/Comparable, java/lang/CharSequence]
    fields count：5
    value 		 [C
    hash 		 I
    serialVersionUID 		 J
    serialPersistentFields 		 [Ljava/io/ObjectStreamField;
    CASE_INSENSITIVE_ORDER 		 Ljava/util/Comparator;
    methods count: 94
    <init> 		 ()V
    <init> 		 (Ljava/lang/String;)V
    <init> 		 ([C)V
    <init> 		 ([CII)V
    <init> 		 ([III)V
    <init> 		 ([BIII)V
    <init> 		 ([BI)V
    checkBounds 		 ([BII)V
    <init> 		 ([BIILjava/lang/String;)V
    <init> 		 ([BIILjava/nio/charset/Charset;)V
    <init> 		 ([BLjava/lang/String;)V
    <init> 		 ([BLjava/nio/charset/Charset;)V
    <init> 		 ([BII)V
    <init> 		 ([B)V
    <init> 		 (Ljava/lang/StringBuffer;)V
    <init> 		 (Ljava/lang/StringBuilder;)V
    <init> 		 ([CZ)V
    length 		 ()I
    isEmpty 		 ()Z
    charAt 		 (I)C
    codePointAt 		 (I)I
    codePointBefore 		 (I)I
    codePointCount 		 (II)I
    offsetByCodePoints 		 (II)I
    getChars 		 ([CI)V
    getChars 		 (II[CI)V
    getBytes 		 (II[BI)V
    getBytes 		 (Ljava/lang/String;)[B
    getBytes 		 (Ljava/nio/charset/Charset;)[B
    getBytes 		 ()[B
    equals 		 (Ljava/lang/Object;)Z
    contentEquals 		 (Ljava/lang/StringBuffer;)Z
    nonSyncContentEquals 		 (Ljava/lang/AbstractStringBuilder;)Z
    contentEquals 		 (Ljava/lang/CharSequence;)Z
    equalsIgnoreCase 		 (Ljava/lang/String;)Z
    compareTo 		 (Ljava/lang/String;)I
    compareToIgnoreCase 		 (Ljava/lang/String;)I
    regionMatches 		 (ILjava/lang/String;II)Z
    regionMatches 		 (ZILjava/lang/String;II)Z
    startsWith 		 (Ljava/lang/String;I)Z
    startsWith 		 (Ljava/lang/String;)Z
    endsWith 		 (Ljava/lang/String;)Z
    hashCode 		 ()I
    indexOf 		 (I)I
    indexOf 		 (II)I
    indexOfSupplementary 		 (II)I
    lastIndexOf 		 (I)I
    lastIndexOf 		 (II)I
    lastIndexOfSupplementary 		 (II)I
    indexOf 		 (Ljava/lang/String;)I
    indexOf 		 (Ljava/lang/String;I)I
    indexOf 		 ([CIILjava/lang/String;I)I
    indexOf 		 ([CII[CIII)I
    lastIndexOf 		 (Ljava/lang/String;)I
    lastIndexOf 		 (Ljava/lang/String;I)I
    lastIndexOf 		 ([CIILjava/lang/String;I)I
    lastIndexOf 		 ([CII[CIII)I
    substring 		 (I)Ljava/lang/String;
    substring 		 (II)Ljava/lang/String;
    subSequence 		 (II)Ljava/lang/CharSequence;
    concat 		 (Ljava/lang/String;)Ljava/lang/String;
    replace 		 (CC)Ljava/lang/String;
    matches 		 (Ljava/lang/String;)Z
    contains 		 (Ljava/lang/CharSequence;)Z
    replaceFirst 		 (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
    replaceAll 		 (Ljava/lang/String;Ljava/lang/String;)Ljava/lang/String;
    replace 		 (Ljava/lang/CharSequence;Ljava/lang/CharSequence;)Ljava/lang/String;
    split 		 (Ljava/lang/String;I)[Ljava/lang/String;
    split 		 (Ljava/lang/String;)[Ljava/lang/String;
    join 		 (Ljava/lang/CharSequence;[Ljava/lang/CharSequence;)Ljava/lang/String;
    join 		 (Ljava/lang/CharSequence;Ljava/lang/Iterable;)Ljava/lang/String;
    toLowerCase 		 (Ljava/util/Locale;)Ljava/lang/String;
    toLowerCase 		 ()Ljava/lang/String;
    toUpperCase 		 (Ljava/util/Locale;)Ljava/lang/String;
    toUpperCase 		 ()Ljava/lang/String;
    trim 		 ()Ljava/lang/String;
    toString 		 ()Ljava/lang/String;
    toCharArray 		 ()[C
    format 		 (Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/String;
    format 		 (Ljava/util/Locale;Ljava/lang/String;[Ljava/lang/Object;)Ljava/lang/String;
    valueOf 		 (Ljava/lang/Object;)Ljava/lang/String;
    valueOf 		 ([C)Ljava/lang/String;
    valueOf 		 ([CII)Ljava/lang/String;
    copyValueOf 		 ([CII)Ljava/lang/String;
    copyValueOf 		 ([C)Ljava/lang/String;
    valueOf 		 (Z)Ljava/lang/String;
    valueOf 		 (C)Ljava/lang/String;
    valueOf 		 (I)Ljava/lang/String;
    valueOf 		 (J)Ljava/lang/String;
    valueOf 		 (F)Ljava/lang/String;
    valueOf 		 (D)Ljava/lang/String;
    intern 		 ()Ljava/lang/String;
    compareTo 		 (Ljava/lang/Object;)I
    <clinit> 		 ()V
    
    Process finished with exit code 0

> 本文在开源项目：[https://github.com/Android-Alvin/Android-LearningNotes][https_github.com_Android-Alvin_Android-LearningNotes] 中已收录，里面包含不同方向的自学编程路线、面试题集合/面经、及系列技术文章等，资源持续更新中…

[https_github.com_Android-Alvin_Android-LearningNotes]: https://links.jianshu.com/go?to=https%3A%2F%2Fgithub.com%2FAndroid-Alvin%2FAndroid-P7%2Fblob%2Fmaster%2FAndroid%25E5%25BC%2580%25E5%258F%2591%25E8%25BF%2598%25E4%25B8%258D%25E4%25BC%259A%25E8%25BF%2599%25E4%25BA%259B%25EF%25BC%259F%25E5%25A6%2582%25E4%25BD%2595%25E9%259D%25A2%25E8%25AF%2595%25E6%258B%25BF%25E9%25AB%2598%25E8%2596%25AA%25EF%25BC%2581.md