Java中将String类型转换为int类型的五种方法及常见问题分析

String myString = "1234";
int foo = Integer.parseInt(myString);

int foo;
try {
    foo = Integer.parseInt(myString);
} catch (NumberFormatException e) {
    foo = 0;
}

String str = "1234";
Integer x = Integer.valueOf(str);

int y = Integer.valueOf(str);
// 或者
int z = Integer.valueOf(str).intValue();

import org.apache.commons.lang3.math.NumberUtils;

int num = NumberUtils.toInt("1234");

int num = NumberUtils.toInt("abc", 0); // 如果解析失败，返回0

import com.google.common.primitives.Ints;
import java.util.Optional;

Integer fooInt = Ints.tryParse("1234");
Optional<Integer> optionalInt = Optional.ofNullable(fooInt);
int result = optionalInt.orElse(0);

public static int strToInt(String str) {
    int i = 0;
    int num = 0;
    boolean isNeg = false;

    // 检查负号
    if (str.charAt(0) == '-') {
        isNeg = true;
        i = 1;
    }

    // 处理每个字符
    while (i < str.length()) {
        num *= 10;
        num += str.charAt(i++) - '0';
    }

    if (isNeg) {
        num = -num;
    }

    return num;
}

import com.google.common.primitives.Ints;
import org.apache.commons.lang3.math.NumberUtils;
import java.util.Optional;

public class StringToIntConversion {
    public static void main(String[] args) {
        String str = "1234";

        // 使用Integer.parseInt()
        try {
            int num1 = Integer.parseInt(str);
            System.out.println("Integer.parseInt(): " + num1);
        } catch (NumberFormatException e) {
            System.out.println("Integer.parseInt() 解析失败");
        }

        // 使用Integer.valueOf()
        Integer num2 = Integer.valueOf(str);
        System.out.println("Integer.valueOf(): " + num2);

        // 使用NumberUtils.toInt()
        int num3 = NumberUtils.toInt(str);
        System.out.println("NumberUtils.toInt(): " + num3);

        // 使用Ints.tryParse()
        Integer num4 = Ints.tryParse(str);
        Optional<Integer> optionalInt = Optional.ofNullable(num4);
        int result = optionalInt.orElse(0);
        System.out.println("Ints.tryParse(): " + result);

        // 手动实现转换
        int num5 = strToInt(str);
        System.out.println("手动实现转换: " + num5);
    }

    public static int strToInt(String str) {
        int i = 0;
        int num = 0;
        boolean isNeg = false;

        if (str.charAt(0) == '-') {
            isNeg = true;
            i = 1;
        }

        while (i < str.length()) {
            num *= 10;
            num += str.charAt(i++) - '0';
        }

        if (isNeg) {
            num = -num;
        }

        return num;
    }
}

String str = "abc123";
String filteredStr = str.replaceAll("[^\\d]", "");
try {
    int num = Integer.parseInt(filteredStr);
    System.out.println("过滤后的结果: " + num);
} catch (NumberFormatException e) {
    System.out.println("解析失败");
}

String str = "2147483648";
try {
    long num = Long.parseLong(str);
    System.out.println("使用Long.parseLong(): " + num);
} catch (NumberFormatException e) {
    System.out.println("解析失败");
}