Java throw与throws #

throw new 异常类型("异常信息");

public void setAge(int age) {
    if (age < 0 || age > 150) {
        throw new IllegalArgumentException("年龄必须在0-150之间");
    }
    this.age = age;
}

// 抛出运行时异常
public void checkNotNull(Object obj) {
    if (obj == null) {
        throw new NullPointerException("对象不能为空");
    }
}

// 抛出检查异常
public void readFile(String path) throws FileNotFoundException {
    if (path == null) {
        throw new FileNotFoundException("文件路径不能为空");
    }
}

返回类型 方法名(参数列表) throws 异常类型1, 异常类型2 {
    // 方法体
}

public void readFile(String path) throws FileNotFoundException, IOException {
    FileInputStream fis = new FileInputStream(path);
    // 读取操作
}

public void copyFile(String src, String dest) 
        throws FileNotFoundException, IOException {
    try (FileInputStream fis = new FileInputStream(src);
         FileOutputStream fos = new FileOutputStream(dest)) {
        // 复制操作
    }
}

// throw：抛出异常
public void method1() {
    throw new RuntimeException("错误");
}

// throws：声明异常
public void method2() throws IOException {
    // 可能抛出IOException
}

// 组合使用
public void method3() throws IllegalArgumentException {
    if (invalid) {
        throw new IllegalArgumentException("参数无效");
    }
}

public void method1() throws Exception {
    method2();
}

public void method2() throws Exception {
    method3();
}

public void method3() throws Exception {
    throw new Exception("原始异常");
}

public void outer() {
    try {
        inner();
    } catch (IOException e) {
        System.out.println("捕获到异常: " + e.getMessage());
    }
}

public void inner() throws IOException {
    throw new IOException("内部异常");
}

class Parent {
    public void method() throws IOException { }
}

class Child extends Parent {
    // 正确：抛出相同异常
    @Override
    public void method() throws IOException { }
    
    // 正确：抛出子类异常
    // @Override
    // public void method() throws FileNotFoundException { }
    
    // 正确：不抛出异常
    // @Override
    // public void method() { }
    
    // 错误：抛出父类没有的检查异常
    // @Override
    // public void method() throws SQLException { }
    
    // 正确：可以抛出运行时异常
    // @Override
    // public void method() throws RuntimeException { }
}

// 参数校验：使用运行时异常
public void setName(String name) {
    if (name == null || name.isEmpty()) {
        throw new IllegalArgumentException("姓名不能为空");
    }
    this.name = name;
}

// 业务异常：使用检查异常
public void withdraw(double amount) throws InsufficientBalanceException {
    if (amount > balance) {
        throw new InsufficientBalanceException("余额不足");
    }
    balance -= amount;
}

// 不推荐
throw new IllegalArgumentException("错误");

// 推荐
throw new IllegalArgumentException("年龄 " + age + " 不在有效范围内(0-150)");

public void loadData() throws DataLoadException {
    try {
        readFromFile();
    } catch (IOException e) {
        throw new DataLoadException("数据加载失败", e);
    }
}

public void process(String input) {
    // 尽早检查和抛出异常
    if (input == null) {
        throw new IllegalArgumentException("输入不能为空");
    }
    if (input.isEmpty()) {
        throw new IllegalArgumentException("输入不能为空字符串");
    }
    
    // 正常处理
    doProcess(input);
}