JVM内存与垃圾回收篇第5章虚拟机栈

public class StackErrorTest {
    private static int count = 1;
    public static void main(String[] args) {
        System.out.println(count);
        count++;
        main(args);
    }
}

-Xss1024m		// 栈内存为 1024MBS
-Xss1024k		// 栈内存为 1024KB

public class StackErrorTest {
    private static int count = 1;
    public static void main(String[] args) {
        System.out.println(count);
        count++;
        main(args);
    }
}

public class StackFrameTest {
    public static void main(String[] args) {
        StackFrameTest test = new StackFrameTest();
        test.method1();
    }

    public void method1() {
        System.out.println("method1()开始执行...");
        method2();
        System.out.println("method1()执行结束...");
    }

    public int method2() {
        System.out.println("method2()开始执行...");
        int i = 10;
        int m = (int) method3();
        System.out.println("method2()即将结束...");
        return i + m;
    }

    public double method3() {
        System.out.println("method3()开始执行...");
        double j = 20.0;
        System.out.println("method3()即将结束...");
        return j;
    }
}

method1()开始执行...
method2()开始执行...
method3()开始执行...
method3()即将结束...
method2()即将结束...
method1()执行结束...

  public void method1();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #6                  // String method1()开始执行...
         5: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: aload_0
         9: invokevirtual #8                  // Method method2:()I
        12: pop
        13: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
        16: ldc           #9                  // String method1()执行结束...
        18: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        21: return
      LineNumberTable:
        line 16: 0
        line 17: 8
        line 18: 13
        line 19: 21
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      22     0  this   Lcom/atguigu/java1/StackFrameTest;
1234567891011121314151617181920212223
  public int method2();
    descriptor: ()I
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=1
         0: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #10                 // String method2()开始执行...
         5: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: bipush        10
        10: istore_1
        11: aload_0
        12: invokevirtual #11                 // Method method3:()D
        15: d2i
        16: istore_2
        17: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
        20: ldc           #12                 // String method2()即将结束...
        22: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        25: iload_1
        26: iload_2
        27: iadd
        28: ireturn
      LineNumberTable:
        line 22: 0
        line 23: 8
        line 24: 11
        line 25: 17
        line 26: 25
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      29     0  this   Lcom/atguigu/java1/StackFrameTest;
           11      18     1     i   I
           17      12     2     m   I
           
  public double method3();
    descriptor: ()D
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=1
         0: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #13                 // String method3()开始执行...
         5: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: ldc2_w        #14                 // double 20.0d
        11: dstore_1
        12: getstatic     #5                  // Field java/lang/System.out:Ljava/io/PrintStream;
        15: ldc           #16                 // String method3()即将结束...
        17: invokevirtual #7                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        20: dload_1
        21: dreturn
      LineNumberTable:
        line 30: 0
        line 31: 8
        line 32: 12
        line 33: 20
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      22     0  this   Lcom/atguigu/java1/StackFrameTest;
           12      10     1     j   D

public class LocalVariablesTest {
    private int count = 0;

    public static void main(String[] args) {
        LocalVariablesTest test = new LocalVariablesTest();
        int num = 10;
        test.test1();
    }

    public void test1() {
        Date date = new Date();
        String name1 = "atguigu.com";
        test2(date, name1);
        System.out.println(date + name1);
    }

    public String test2(Date dateP, String name2) {
        dateP = null;
        name2 = "songhongkang";
        double weight = 130.5;//占据两个slot
        char gender = '男';
        return dateP + name2;
    }
    
}

public static void main(String[] args) {
    if(args == null){
        LocalVariablesTest test = new LocalVariablesTest();
    }
    int num = 10;
}

public void test3() {    this.count++;}

public String test2(Date dateP, String name2) {    dateP = null;    name2 = "songhongkang";    double weight = 130.5;//占据两个slot    char gender = '男';    return dateP + name2;}

//练习：public static void testStatic(){    LocalVariablesTest test = new LocalVariablesTest();    Date date = new Date();    int count = 10;    System.out.println(count);    //因为 this 变量不存在于当前方法的局部变量表中！！    //System.out.println(this.count);}

public void test4() {    int a = 0;    {        int b = 0;        b = a + 1;    }    //变量c使用之前已经销毁的变量b占据的slot的位置    int c = a + 1;}

public void testAddOperation() {    //byte、short、char、boolean：都以int型来保存    byte i = 15;    int j = 8;    int k = i + j;}

 0 bipush 15 2 istore_1 3 bipush 8 5 istore_2 6 iload_1 7 iload_2 8 iadd 9 istore_310 return

public int getSum(){    int m = 10;    int n = 20;    int k = m + n;    return k;}public void testGetSum(){    //获取上一个栈桢返回的结果，并保存在操作数栈中    int i = getSum();    int j = 10;}

// 程序员面试过程中， 常见的i++和++i 的区别，放到字节码篇章时再介绍。public void add(){    //第1类问题：    int i1 = 10;    i1++;    int i2 = 10;    ++i2;    //第2类问题：    int i3 = 10;    int i4 = i3++;    int i5 = 10;    int i6 = ++i5;    //第3类问题：    int i7 = 10;    i7 = i7++;    int i8 = 10;    i8 = ++i8;    //第4类问题：    int i9 = 10;    int i10 = i9++ + ++i9;}

 0 bipush 10 2 istore_1 3 iinc 1 by 1 6 bipush 10 8 istore_2 9 iinc 2 by 112 bipush 1014 istore_315 iload_316 iinc 3 by 119 istore 421 bipush 1023 istore 525 iinc 5 by 128 iload 530 istore 632 bipush 1034 istore 736 iload 738 iinc 7 by 141 istore 743 bipush 1045 istore 847 iinc 8 by 150 iload 852 istore 854 bipush 1056 istore 958 iload 960 iinc 9 by 163 iinc 9 by 166 iload 968 iadd69 istore 1071 return

//第2类问题：int i3 = 10;int i4 = i3++;

12 bipush 1014 istore_315 iload_316 iinc 3 by 119 istore 4

int i5 = 10;int i6 = ++i5;

21 bipush 1023 istore 525 iinc 5 by 128 iload 530 istore 6

public class DynamicLinkingTest {    int num = 10;    public void methodA(){        System.out.println("methodA()....");    }    public void methodB(){        System.out.println("methodB()....");        methodA();        num++;    }}

  public void methodB();    descriptor: ()V    flags: ACC_PUBLIC    Code:      stack=3, locals=1, args_size=1         0: getstatic     #3                  // Field java/lang/System.out:Ljava/io/PrintStream;         3: ldc           #6                  // String methodB()....         5: invokevirtual #5                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V         8: aload_0         9: invokevirtual #7                  // Method methodA:()V        12: aload_0        13: dup        14: getfield      #2                  // Field num:I        17: iconst_1        18: iadd        19: putfield      #2                  // Field num:I        22: return      LineNumberTable:        line 16: 0        line 18: 8        line 20: 12        line 21: 22      LocalVariableTable:        Start  Length  Slot  Name   Signature            0      23     0  this   Lcom/atguigu/java1/DynamicLinkingTest;

Constant pool:   #1 = Methodref          #9.#23         // java/lang/Object."<init>":()V   #2 = Fieldref           #8.#24         // com/atguigu/java1/DynamicLinkingTest.num:I   #3 = Fieldref           #25.#26        // java/lang/System.out:Ljava/io/PrintStream;   #4 = String             #27            // methodA()....   #5 = Methodref          #28.#29        // java/io/PrintStream.println:(Ljava/lang/String;)V   #6 = String             #30            // methodB()....   #7 = Methodref          #8.#31         // com/atguigu/java1/DynamicLinkingTest.methodA:()V   #8 = Class              #32            // com/atguigu/java1/DynamicLinkingTest   #9 = Class              #33            // java/lang/Object  #10 = Utf8               num  #11 = Utf8               I  #12 = Utf8               <init>  #13 = Utf8               ()V  #14 = Utf8               Code  #15 = Utf8               LineNumberTable  #16 = Utf8               LocalVariableTable  #17 = Utf8               this  #18 = Utf8               Lcom/atguigu/java1/DynamicLinkingTest;  #19 = Utf8               methodA  #20 = Utf8               methodB  #21 = Utf8               SourceFile  #22 = Utf8               DynamicLinkingTest.java  #23 = NameAndType        #12:#13        // "<init>":()V  #24 = NameAndType        #10:#11        // num:I  #25 = Class              #34            // java/lang/System  #26 = NameAndType        #35:#36        // out:Ljava/io/PrintStream;  #27 = Utf8               methodA()....  #28 = Class              #37            // java/io/PrintStream  #29 = NameAndType        #38:#39        // println:(Ljava/lang/String;)V  #30 = Utf8               methodB()....  #31 = NameAndType        #19:#13        // methodA:()V  #32 = Utf8               com/atguigu/java1/DynamicLinkingTest  #33 = Utf8               java/lang/Object  #34 = Utf8               java/lang/System  #35 = Utf8               out  #36 = Utf8               Ljava/io/PrintStream;  #37 = Utf8               java/io/PrintStream  #38 = Utf8               println  #39 = Utf8               (Ljava/lang/String;)V

/** * 说明早期绑定和晚期绑定的例子 * * @author shkstart * @create 2020 上午 11:59 */class Animal {    public void eat() {        System.out.println("动物进食");    }}interface Huntable {    void hunt();}class Dog extends Animal implements Huntable {    @Override    public void eat() {        System.out.println("狗吃骨头");    }    @Override    public void hunt() {        System.out.println("捕食耗子，多管闲事");    }}class Cat extends Animal implements Huntable {    public Cat() {        super();//表现为：早期绑定    }    public Cat(String name) {        this();//表现为：早期绑定    }    @Override    public void eat() {        super.eat();//表现为：早期绑定        System.out.println("猫吃鱼");    }    @Override    public void hunt() {        System.out.println("捕食耗子，天经地义");    }}public class AnimalTest {    public void showAnimal(Animal animal) {        animal.eat();//表现为：晚期绑定    }    public void showHunt(Huntable h) {        h.hunt();//表现为：晚期绑定    }}

/** * 解析调用中非虚方法、虚方法的测试 * * invokestatic指令和invokespecial指令调用的方法称为非虚方法 * @author shkstart * @create 2020 下午 12:07 */class Father {    public Father() {        System.out.println("father的构造器");    }    public static void showStatic(String str) {        System.out.println("father " + str);    }    public final void showFinal() {        System.out.println("father show final");    }    public void showCommon() {        System.out.println("father 普通方法");    }}public class Son extends Father {    public Son() {        //invokespecial        super();    }    public Son(int age) {        //invokespecial        this();    }    //不是重写的父类的静态方法，因为静态方法不能被重写！    public static void showStatic(String str) {        System.out.println("son " + str);    }    private void showPrivate(String str) {        System.out.println("son private" + str);    }    public void show() {        //invokestatic        showStatic("atguigu.com");        //invokestatic        super.showStatic("good!");        //invokespecial        showPrivate("hello!");        //invokevirtual        //虽然字节码指令中显示为invokevirtual，但因为此方法声明有final，不能被子类重写，所以也认为此方法是非虚方法。        showFinal();        //invokespecial        super.showCommon();        //invokevirtual        //有可能子类会重写父类的showCommon()方法        showCommon();        info();        MethodInterface in = null;        //invokeinterface        in.methodA();    }    public void info() {    }    public void display(Father f) {        f.showCommon();    }    public static void main(String[] args) {        Son so = new Son();        so.show();    }}interface MethodInterface {    void methodA();}

@FunctionalInterfaceinterface Func {    public boolean func(String str);}public class Lambda {    public void lambda(Func func) {        return;    }    public static void main(String[] args) {        Lambda lambda = new Lambda();        Func func = s -> {            return true;        };        lambda.lambda(func);        lambda.lambda(s -> {            return true;        });    }}

Java：String info = "mogu blog";     		(Java是静态类型语言的，会先编译就进行类型检查)JS：var name = "shkstart";    var name = 10;	（运行时才进行检查）

public class ReturnAddressTest {    public boolean methodBoolean() {        return false;    }    public byte methodByte() {        return 0;    }    public short methodShort() {        return 0;    }    public char methodChar() {        return 'a';    }    public int methodInt() {        return 0;    }    public long methodLong() {        return 0L;    }    public float methodFloat() {        return 0.0f;    }    public double methodDouble() {        return 0.0;    }    public String methodString() {        return null;    }    public Date methodDate() {        return null;    }    public void methodVoid() {    }    static {        int i = 10;    }    public void method2() {        methodVoid();        try {            method1();        } catch (IOException e) {            e.printStackTrace();        }    }    public void method1() throws IOException {        FileReader fis = new FileReader("atguigu.txt");        char[] cBuffer = new char[1024];        int len;        while ((len = fis.read(cBuffer)) != -1) {            String str = new String(cBuffer, 0, len);            System.out.println(str);        }        fis.close();    }}

/** * 面试题： * 方法中定义的局部变量是否线程安全？具体情况具体分析 * *   何为线程安全？ *      如果只有一个线程才可以操作此数据，则必是线程安全的。 *      如果有多个线程操作此数据，则此数据是共享数据。如果不考虑同步机制的话，会存在线程安全问题。 * @author shkstart * @create 2020 下午 7:48 */public class StringBuilderTest {    //s1的声明方式是线程安全的    public static void method1(){        //StringBuilder:线程不安全        StringBuilder s1 = new StringBuilder();        s1.append("a");        s1.append("b");        //...    }    //sBuilder通过参数传递方法内，存在线程不安全的问题    public static void method2(StringBuilder sBuilder){        sBuilder.append("a");        sBuilder.append("b");        //...    }    //操作s1之后，将s1作为返回值返回，存在线程不安全的问题    public static StringBuilder method3(){        StringBuilder s1 = new StringBuilder();        s1.append("a");        s1.append("b");        return s1;    }    //s1的操作：是线程安全的    public static String method4(){        StringBuilder s1 = new StringBuilder();        s1.append("a");        s1.append("b");        return s1.toString();    }    public static void main(String[] args) {        StringBuilder s = new StringBuilder();        new Thread(() -> {            s.append("a");            s.append("b");        }).start();        method2(s);    }}