How to convert a numeric string to an integer

Such as "12345", Convert to 12345 This form

package com.isea.java;
public class Test {
    
    public static void main(String[] args) {
    
        String str = "1234";
 
        Integer num1 = new Integer(str);
 
        int num2 = Integer.parseInt(str);
 
        Integer num3 = Integer.valueOf(str);
 
        System.out.println(num1 + "\t" + num2 + "\t" + num3);//1234 1234 1234
    }
}

The above three methods are all acceptable
About Integer Class should know

Integer a=1;
Integer b=1;
System.out.println(a==b);//true
Integer c=128;
Integer d=128;
System.out.println(c==d);//false

The first output true, The second output false
Because for Integer class When the number is in -128 To 127 In between It can be taken out directly
Here is the source code involves Integer There is a cache
When more than 127 When Equivalent to new Integer(x) 了 == Compared with address So the second one is false

private static class IntegerCache {
    
        static final int low = -128;
        static final int high;
        static final Integer cache[];

        static {
    
            // high value may be configured by property
            int h = 127;
            String integerCacheHighPropValue =
                VM.getSavedProperty("java.lang.Integer.IntegerCache.high");
            if (integerCacheHighPropValue != null) {
    
                try {
    
                    int i = parseInt(integerCacheHighPropValue);
                    i = Math.max(i, 127);
                    // Maximum array size is Integer.MAX_VALUE
                    h = Math.min(i, Integer.MAX_VALUE - (-low) -1);
                } catch( NumberFormatException nfe) {
    
                    // If the property cannot be parsed into an int, ignore it.
                }
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);

            // range [-128, 127] must be interned (JLS7 5.1.7)
            assert IntegerCache.high >= 127;
        }

        private IntegerCache() {
    }
    }